This is an old thread, but even though I'm a new roaster with next to no experience, I'd like to add my comments about using the aluminum stovetop whirleypop style popcorn popper for roaster.
I'm using the thin aluminum popper with the plastic gears and the thin wire agitator. I drilled a hole in the top for a dial thermometer. Otherwise I've made no changes to it. I have a gas stove indoors with a very powerful exhaust that works quite well, but I found after one roast that there was still a lingering heavy roast oder and some mess from the chaff, so I decided to move my roasting operation outdoors. I'm now roasting on a propane Expedition 3X Triple Burner Stove
that I bought from Costco back in 2004.
This stove works even better than the natural gas stove in my kitchen. It produces a lot more BTU than my kitchen stove, so I can use it at a low setting. Propane burns hotter than natural gas. I set it just above the low setting, not quite halfway to medium. The burner is several inches below the grate, so the flames aren't actually touching the aluminum popper. The popper heats up quickly and the temperature remains stable and then starts climbing slowly after then initial temperature drop when the beans are added. I don't have to move the popper on or off the heat or adjust the flame height during the roast.
I have not had any problems with scorching, and my roasts are pretty even. The plastic gears are holding up so far, but I have only roasted a few batches. I do have my doubts that the gears will hold up in the long run. I'm also concerned that the handle may come off. It is not very securely held on. I am not too worried about it though. These pots are cheap. If I can't fix something that goes wrong, I'll just toss it and buy another one.
I don't think you need to go for the heavier SS pot if you roast on a propane stove like mine, because scorching won't be an issue as long as you crank the whole time. I bought one of those heavy bottomed SS pots to use for popcorn since I'd appropriated the aluminum plastic-geared one for roasting coffee. I like the lighter weight aluminum one better, even for popcorn. Of course, I don't want roasted coffee flavored popcorn, so I'll just keep using the new SS one for popcorn. A big problem with the heavier SS popper that I bought is the gear quality. The gears are made of aluminum. They are soft, and I very much doubt that they'll hold up as long as the plastic gears. Brass would have been a better choice for the gears.
All in all, these stovetop whirleypop style poppers are all very cheaply made from cheap low-quality components. Fortunately, they are also cheap to purchase, especially if you just buy the thin aluminum one with the plastic gears, which seems to work just fine. I think if it works for a year, you get your money's worth.