Well...Its slower for sure. The crotchy stuff that wont fit...obviously gets cut and tossed to the side.
Its great for pruning. but the bigger stuff needs to be nice and straight. Sometimes,I will make little 1/2 cuts on branch unions so that they will fold when the feed wheel grabs it and pulls it in. Everything over 5 inches is firewood. Thats just the way it is.
The 625 is not for everyone. I run a small outfit (usualy just me) so the 625 is a good call for me right now.
I swap bed knife edge EVERY time i do a knife change.
I make the gap between the bedkife and knives paper thin.
I keep rocks and dirt from going through.
One time I had to unwrap a bunch of fiborous stuff from around the main bearings. (that held up the machine quite a bit). Most of the power is in the momentum of the cutter wheel, not from the power of the "mighty" 27 horse Kohler

If your bearings are shot or of the wheel dont spin freely, then yes the machine will bog down.
um....I dont know what else say other than the fact that I do admit its not as fast as a bigger machine.
I still like it
