Hi Nightguy,
I believe a drum roaster uses convectional heat and stirs the beans for an even roast by drum rotation. The beans heat slower so longer roasts are capable and the drum size is larger in comparison to a fluid bed (pop corn popper style forced hot air) roaster. I think the roasts you can get with a drum are toastier and perhaps sweeter given that it's easier to more fully caramelize a bean's sugar and take it past 1st crack without burning it.
A fluid bed, popcorn popper style roaster uses forced air to both roast and circulate the beans. They roast much faster and much more evenly since the forced air is constantly circulating all around the beans. However the increased degree of circulation and the smaller batch size of a fluid bed makes for a much faster roast. It's difficult to do a long roast with a fluid bed and the rest periods between 1st and 2nd crack end up being short, sometimes very short. Fluid bed roasts tend to be much brighter than drum roasts.
Fluid bed roaster like the Fresh Roast, i Roast, Zach & Dani's, popcorn poppers...are less expensive than drum roasters. They're also smaller and take up about the same space as a coffee maker.
So, I guess it depends on how much you want to roast at any one time, what kind of roast you prefer and how much you're willing to spend.
If you don't want to spend a lot of money there are other ways to roast beans besides a dedicated machine.