I have asked Square support, but I was looking for people that use it in real time before I pull the trigger on 1.3.0 update.
Plus it looks like they haven't tested it with any upgrade since 1.2.16 and Fast Checkout is a No Go
AbanteCart 1.2.x installed (tested up to AbanteCart 1.2.16). [There is no current support for AbanteCart's FastCheckout.]