Used to have straight talk with smart phone before jumping to Sprint.
They do have legit smart phones, and they work like..well legit smart phones. Coverage was also generally good because they piggy back off other networks, and seem to jump to a stronger network then their default one when needed without issue.
Problem I had with them was a couple fold. Older phones, wife and I don't need the shiniest phones but we wanted newer then straight talk was offering. Call quality, in general, was not as good as better phones on the actual carriers network. And their "unlimited" plan isn't unlimited. It has an arbitrary cap that they refuse to disclose, giving different numbers to different people when they get cut off and call to complain. Their TOS says unspecific mumbo jumpo about normal use or some such. In short, if you stream music and such, your SOL&JWF. Also, tethering isn't even an option. Their CS makes Verizon look like polished professionals.
In short, their not a bad option if you want to go into the smart phone Android arena. But you'll be doing so on older phones, piggy backing onto another network with reduced quality, and subject to an arbitrary data cap they seem to make up as they go along.
