More and more places require a deposit for bookings, because so many are made and then folks don't turn up. The habit of booking multiple 'options' and ditching them at short notice is parasitic and noxious, and this was always going to happen.
So will restaurateurs trust Duplex? Especially if they know it's a Google product? How will it negotiate deposits? Will a deposit paid by duplex be honoured? Refunded? Disavowed? Many English speakers seem to have difficulty with foreign accented-English (even when spoken, as is sometimes the case, by people with a better vocabulary and grammar than their English interlocutors)—especxially Indian, for some reasons—so will Duplex do any better, when negotiating a slightly later booking with the Taj Mahal for Friday evening?
And when we've got past those problems, how long before malware, spyware and all the other "dark fuckery of the human heart"*¹ kicks in? When the TM says they'll keep the three deposits committed to by Duplex because it's not their fault if your rogue/contaminated/abused system made bookings in your name? Or blocks you for nuisance bookings that you keep not turning up to? Or insists that you're not getting the seven o'clock table you thought you'd booked, because Rashinder and Duplex agreed to eleven o'clock instead? Or you get irritated calls from 17 different places asking what the hell is going on, because someone pranked your infected system and made a shedload of random bookings for you? Whenl your Significant Other queries a romantic dinner for two that she wasn't invited to, will you earnestly explain that Google must have gone rogue and made the booking for you? Duplex as alibi?
The failure and chaos modes are numerous. No one thought email would be a harbinger of so much wasted time and chaos 30 years ago, but look where we got to. And email is actually useful, unlike a system designed for people too paralytically lazy to pick up a phone or visit a website. If normal use doesn't create major problems, you may be certain that once the vandals and Black Hats get involved, you're in for a wild ride. And that doesn't even address the idiocy of giving the laughably named Don't Be Evil with yet another invasion-of-privacy vector ...
*¹ Nod to Stephen King