I am very happy with the APC 14x4W on my YS 63 powered Flip 3D. I use 30% nitro fuel though.
I think if you use lower nitro fuel the engine is not going to have the extra power it needs to turn the 14x4W good and that's why some of you are not liking it.
I used to fly on 15% nitro, but have switched to 30% now and just love it. What a difference!
I was constantly adjusting the engine on 15% nitro, but now on 30% nitro I never have to touch the engine settings and the engine runs so much nicer. It is worth the extra $6-$7 a gallon to me.

Jim