I also have the Chef's Choice 615. I paid $150 for it, shipped, from
Amazon. I've had it for three years. I use it at least once a week. It does have plastic gears, but I've never had it even begin to stall. I usually semi-freeze my meat before I slice it (or only partially defrost the meat, if it is already frozen) and can get slices that are transparently thin, if I really want it that thin.
I cut cheese all the time, although I've never tried to slice a thick block of Costco sharp cheddar. I suspect it would slice just fine. I've occasionally done vegetables (carrots, for instance), but I have a mandolin that is a better tool for that job.
It is a pain to clean up, but having not owned any other slicer prior to this, I don't know if other slicers are easier to clean. I suspect they all take quite a bit of effort because of all the moving parts.
The unit comes with a serrated blade, but I did buy a non-serrated blade which is supposed to let you get thinner slices on some meats. I use it about 50% of the time, but don't notice any appreciable difference. If I had to do it over again, I'd still get the 615 (I still like it after three years), but I wouldn't bother with the extra blade.