they're just shops. If they don't sell something you want, then that's something they could do better. But you can't judge one by another; different ones stock different things and have different staff; you'll just have to check it out when it opens. And don't forget to say farewell to all the small traders it'll put out of business.
Best thing - they sell the stuff you could usually pick up in Tesco anyway (a selection of them at least, obviously they don't carry as many items as a Tesco Extra!)
Worst thing - stuff id more expensive than the normal Tesco and as jno says, they put the small shopkeepers out of business. (not good, I work for one).