This is the Ford vs Chevy thread but, here's my opinion anyway. I've got two TT Pro 46s and two TT Pro 61s one 46 FX one 55 AX one 75 AX and one 91 FX. For the difference in the price I would go with the TT Pro engine. They are just as easy to break in, tune and keep up as the OS engines. Two of the TT Pro engines were my first engines. They have more gallons through them than I care to think. My trainer proably gets more flights on it still than any of the other planes and all I have done to it is one glow plug. It'll crank everytime with a chicken stick. One flip if it's above freezing. Might take two if it's cold. It's a 61. Getting parts for the OS engines has been simple. You can call Tower and they will get them on the way. I don't know how hard it will be to get parts for the TT engines, I've not needed any yet.