You guys oughta read my last post. I stated that I just got the machine, did do a few stumps that could have been done with a normal portable.........I will continue to do so.
Hoosier, perhaps your ground isn't as rocky as ours......Even the rock teeth dull and chip badly and easily. The only difference is the rake angle, not the hardness of the carbide----I think. I'm going to talk to Keith to see if there's anything that could be done to improve the durability of the teeth.
But, on a reasonable size stump, as Hoosier said, if the teeth are sharp (the normal teeth which have a sharper rake angle than the rock teeth), the AM is very fast cutting, and could well be faster than a 25 horse 252 or Rayco,.
On a typical stump in our rocky soil, I spend might 25 minutes digging and 15 minutes grinding. With a 252 sized machine, it would be more like 10 minutes of digging, 15 minutes grinding, and 15 minutes load/unload.
My main business is tree work, not stumps. I got the AM to be able to do stumps that no one else can do...My 3 stumper subs are now referring jobs to me, as are a couple of tree services. I don't use the AM much, but am told by Keith of AM that there are a bunch of users that keep busy with the machine and make a boatload of $ with it.
Yes, those ~13 hp small do it yourself grinders are worthless compared to an AM. Won't work on steep slopes, relatively bulky,less rpm, so less grinding speed.....My unit has plenty of power, so I'm going to keep the 9 hp 3120 stock. I doubt my 13 hp modded 3120 would be any faster....for one thing, its muffler wouldn't fit...and would be obnoxiously loud. The 4800 rpm AM has so much wheel speed and inertia that it allows throttle blipping...don't have to run it at continuous full throttle.