2 St Anne’s Court, London W1 (020 7437 0566). Meal for two, including wine and service: £80

This week’s restaurant comes from the people who brought us Beast. You remember Beast. The one with the king crabs and the Nebraskan steaks and the over-engineered tables and the bill that made me feel like my scrotum had been put in an un-lubricated vice. So now you’re salivating – not at the thought of the food, but at the prospect of some brutal knob-gag-strewn take-down. Well, put your tongue away. Wipe your mouth on a napkin. Sit back and take note.

Beast may be irredeemably silly. One of the team later described it to me as the McLaren F1 supercar of the restaurant world, and you don’t get much sillier than that. But the people aren’t. To recap, the Moscow-born group started with their superlative steak restaurants, Goodman. They still vie with Hawksmoor for the title “best in show” when it comes to slabs of grilled cow. Next they launched Burger and Lobster, selling both at £20 and creating such a queue that they needed a pager system to deal with those prepared to wait.

Now they have this new fish place. Once again they have installed a pager system, though as yet it isn’t needed. If there’s justice it should be, for Rex and Mariano is a bloody good idea, very nicely executed: quality seafood, presented to the best of its advantage, in a manner that keep costs low. We’ll get to that in a moment. That it’s a little quiet at present raises interesting questions over the power of location. We know there’s a restaurant boom in London right now, making prime sites in prime territory very expensive. In theory there should not be such a thing as a bad site in London’s Soho.

But this low-ceilinged, wide room on St Anne’s Court, a pedestrian cut-through between Wardour and Dean Streets, has always struggled. In my memory it has been an American deli, some sort of Mexican cantina, a tapas bar and, most recently, a scary bar called Vodka Revolution which looked to me like Dante’s fourth circle of hell. I never set foot in it but, looking at the website of its remaining siblings, I see it included fish and chips, chicken katsu, a vodka chicken pizza and something, rather terrifyingly, called “hot pork balls”. They also had a burger called the Bourbon Bad Boy. Calling any menu item a “bad boy” is excuse enough for arson or, failing that, laughing and pointing. After 15 years in this gig I have learnt that it’s sometimes OK to decide a menu is a bad idea without ever eating anything from it. Whatever the reason for its closure we can celebrate the fact that Soho is now spared its vodka chicken pizza.

Now it’s a site where you will eat well. It has the white-tiled, industrial-ducting look that is obligatory for fish restaurants, the space fringed by a series of stations: a raw bar, a plancha, an oyster-shucking bar and so on. As to its name, that comes from the involvement of the highly regarded Chelsea fishmonger Rex Goldsmith, and a Sicilian chap who is helping bring in the best of the catch from over there. That includes the red prawns which were one of the best things we ate at Beast, and which here are on the menu for £4 less. Price is key.

Rock oysters are £1.50 a pop, which isn’t much over retail price. (By comparison the cheapest rocks at the very lovely Bentley’s on Swallow Street are just over £2.50 each). Generous portions of carpaccio, tartare and so on are just £7 and heaps of clams are £6. How do they manage this? Partly it’s a volume operation with economies of scale, but mostly it’s by replacing half the waiters with iPads. It’s a trick that’s been tried elsewhere before, but here the interface is smarter, and the ordering system so efficient that it really does change the rhythm of the meal. You order as you go, until you’re done. Naturally, real human beings do pop by every now and then to bring the plates, and they will still ask you how everything is. But they do it with such grace and charm you can’t resent them for it.

Of course, if the food didn’t hit its mark the rest of this would be irrelevant, but it does. It’s clean and uncluttered. Of the three things we try from the raw bar the best is cubes of tuna tartare with avocado purée and a punchy dressing of chilli, chives and, best of all, sesame oil. It has us fighting over the last bits. A sea bass carpaccio, simply dressed with olive oil, lemon and a little tomato, is a close-run second. A salmon ceviche with a fennel salad is a little relentless, but I think that has to do with the lumbering nature of the fish. This food feels good for you.

The salty red prawns are the stars just as they were at Beast. If you’re trying to judge someone’s character bring them here and order a plate of these prawns. If your companion does not start sucking at the heads, send them politely on their way. They are not greedy enough, and will prove unsatisfying company. Happy to help. The crimson puddle of sweet-salty juices must not be allowed to go to waste and though the £3 charge for bread baked on the premises looks enthusiastic, it’s a varied plateful. The worst you can say is it’s trying a little too hard, when you want just one utilitarian bread that will do the job. Keep it close by for the wine-and-butter slick left behind by the clams. Deep-fried courgettes are the addictive stuff that a stay at the Priory is made of.

Dessert is a complete afterthought. You can have lemon sorbet with or without limoncello. And that’s it. It’s good lemon sorbet and a nice limoncello, but if they can bake their own bread they can bake a few other things, too. The wine list is short. On the upside it comes in half-carafes. On the downside it’s a little overpriced, with a Picpoul working out at £30 a bottle; back at Bentley’s, where you get linen tablecloths and waiters with notepads, it’s over a quid cheaper. But I am being picky. Rex and Mariano doesn’t re-invent the restaurant. But it does create a space I could sneak into for a crafty plate of prawns and solo head suckage. Let’s put it this way: Rex and Mariano is no Beast. That’s a recommendation.

Jay’s news bites

■ The outpost of the small Wright Brothers restaurant group in London’s Spitalfields offers you the chance to choose your dinner while it still has a pulse. The restaurant is dominated by a large tank of crabs and lobsters. The choice of oysters is terrific and there are also some very good cooked dishes, especially the crab croquettes. What’s more, they now do chips (thewrightbrothers.co.uk).
■ After 46 years the Spaghetti House at 77 Knightsbridge is to close, having been told to surrender their lease by the landlord. The restaurant is infamous as the site of a five-day siege in 1975 after a botched robbery which resulted in staff being held hostage. The other 10 branches of the chain are trading successfully and they are looking for a replacement site nearby (spaghettihouse.co.uk).
■ Need a special gift for Valentine’s Day? Sixty chefs and chocolatiers are creating special boxes of chocolates to be auctioned off via eBay in aid of Galvin’s Chance, an into-work programme for disadvantaged young people (chocsforchance.org).

Email Jay at jay.rayner@observer.co.uk. Follow Jay on Twitter@jayrayner1