Basic dumb phone for a kid

Any recommendations for a basic (voice and text only) phone that would work with Red Pocket?

I'm looking at this AGM phone:

But I can't get a straight answer from either Red Pocket nor AGM whether it would actually work with Red Pocket. It just says it's compatible with T-Mobile, and Red Pocket does use T-Mobile's network, but will it work?

I'm open to other suggestions - as basic as possible and long battery life would be best.