I was recently (a few months ago) at Gordon Ramsey new restaurant in Vegas. They pull out iPads for your wine and beer selection. They would leave it at the table and you could look through the different wines, the regions they came from, how they were made, etc... Same with the beers. It was interesting, but honestly felt like a novelty. Super cumbersome and sort of gave you too much to read. Made the choice harder (for me and my party at least)...

Square seems to be the go-to AFAIK.. they probably have the widest following in terms of absolute number of businesses adopting them. I could be wrong though.

The Square register was a huge flop with most merchants (though they are addressing these issues with more recent updates). Most merchants I've interviewed that use an iPad as a POS solution have tried it, and dumped it for something that actually met their needs. Again, they are addressing these issues, but that was the feedback I received less than 6 months ago.

Anecdotally:

I've eaten at local places that used Square. I have no idea if they're happy customers.

I've seen increased use of Square at our local public farmers markets. The guy I buy my beef from loves his. It's lower initial cost, higher transaction cost, and super easy to use.

(I support any disruption that eats into the VISA/MasterCard/Etc oligarchy.)

Can you expand on why it was such a flop with merchants ?

Sorry, I don't have much info other than it didn't have the critical features they needed in order for it to be useful. The details of those features I never asked about. What I can tell you is that I mainly spoke with cafes, restaurants and other food service related merchants. Only spoke with a handful of retail merchants... Hope that helps!