Yes I too use an Alpine Magnum and when I saw the ST661 last year and I must admit it looked like a good replacement for my Magnum, lighter and more compact too. But having used one and talking to a couple of users we all seem to be complaining of the same issue and that is that there seems to be a fundamental problem with the "Bite". When you want to be grinding into the stump the wheel has little bite and likes to spin a lot making it unnecessarily hard work, something is not quite right with it yet. You do have to exert force and really push and force it in towards the stump and with no spike leg like the Magnum you have to have one foot firmly planted on the wheeled leg at the same time as exerting force, maybe just a different technique to learn but it does lack the bite without a doubt, and Predator seem to know but be in denial or at least the feedback has gone back to them and wasn't accepted.
Theres a 3 month old one for sale on eBay right now as the guy has given up with it and i believe Predator replaced the first one he had as it was faulty and he downgraded it but still not happy so he's put it up for sale and gone back to his previous machine. Maybe Predator will read this and take the feedback on board and refine the design, Im sure it could make all the difference if it could do the same workload as a Magnum at half the wight size and cost it could be a winner.... but in my opinion just not yet and I held back from buying one because of that.
