I have not learned to fully trust my Maasdam rope puller yet. It has slipped on me a couple of times, even on 3 strand, and it does not work well for a hard pull using double braid or kernmantle. My bull ropes are 5/8 double braid, so I have to put in a section of 1/2" 3 strand to use the rope puller. I think that gets the safe working load down to 5 or 6 hundred pounds.
I have a Griphoist I dearly love. It runs on 7/16 wire rope much the same as the rope puller runs on a rope, except the wire rope runs through it without a bend. It works with a leveraged brake system, harder you pull the harder the brakes grab. It weighs a good bit more than the rope puller, but I can still get it up in a tree, and it is much more reliable. 4,000 lbs safe working load on single part line. I think that is about the same amount of pull I get with my 4WD 3130 Kubota on dry ground. It is slower than the rope puller, because of the mechanical advantage.
I guess each has its place, but like I said - I dont trust the rope puller for anything critical. I dont do it, but I would be willing, to hang my life on the Griphoist.
Ekka - I'll be rigging the Griphoist for a pull on a live oak this weekend. I'll try to remember to get a picture for you.