PS Vita Reviews just finished their play of the Vita's newest tower-defense games. Here are their final thoughts on Medieval Defenders:
"Medieval Defenders is a basic Mobile-to-Vita transition. On the downside, the game pressures you with micro-transactions, there are no button controls, some of the touch controls don’t work as well as they should, and the game only lasts a few hours. Past this is a decent game for the tower defense fanatic to waste some time with."