I've done the similar Best Buy discount for Simple Mobile, and resold the Simple Mobile refill card to reduce my phone cost. (I got a cheap BLU device to use as a backup phone, currently loaded with a FreedomPop SIM.) I think for most here, the MintSim offer is easily the best of the current promos.
The details for each vary somewhat. The value comes either from being able to use the refill card, or being willing to resell it. (I'll note that when I looked at it, the Cricket offer specifically excluded BLU phones.)