The low tech, but important sway vote for many is that the price for a 3ph model is usualy more expensive than for the same spec'd one that comes with the same but with the addition of a free engine, wheels, filter, etc.. I suppose if you want to put hours on your tractor, you could still buy a complete gas splitter, and either tow it with the tractor, or carry it in the loader. I say the smart money says get the gas powerd splitter and use your tractor for other things.
Come time to sell, the gas splitter will sell to anyone who wants to split = more$ back to you. The 3ph model only sells to a small fraction who have a tractor and want that style. Also don't forget, you are making a big expensive 20 -50hp machine rack up hours doing the work a 7hp engine can do. Most of that time the cylinder is either retracting which takes about 1/2hp, or is sittting still, or is splitting which on most pieces of wood only takes 1-5hp. Same logic goes for pto gennies.