I started a thread about this recently. I think the general consensus was that UWeapon should only be used if you somehow manage to exhaust all 7000 questions in UWorld, Kaplan, and USMLERx.
I got a UWeapon subscription for free with my DIT course, but I haven't activated it yet. I don't think I'll waste my time with it... I still have enough questions left over in Kaplan and UW.