I tried the 12.25x3.75 prop on my thunder tiger 46 w/ stock muffler and baffle removed. It would turn the prop fine, but it was sluggish on spool up.

I had it on for about 2 minutes during a flight, I landed and switch props. I have read that some people have great success w/ 12.25 prop. but others do not. Could be the altitude, fuel, etc.

but I have tried the 12.25 on a ST45 w/ stock muffler, and a TT46 w/ stock muffler w/ baffle removed. And I didn't like it. I swapped back to a 11x4APC.
But I use 11x4APC, 11x5APC, 11x4.5APC. that is what works best for me.

Also tried the 12.25 on my brother OS46 and his magic, hated it. Swapped back to 11x4.5APC. Turn it great, but spool up to slow. But w/ a 11x4.5, throttle transistion was instant. Vertical pull was better to. Hovering was easier, because I could bump the throttle and motor would increase instantly.

I have a friend that has 2 of the same brand and size motors, w/ same fuel, on same day, 1 would spin the 12.25 great, and the other was sluggish.