I really don't understand the pop corn popper as a roaster in its stock form.
Roasting beans at a high heat with no temp control is a bit like throwing anything you are cooking in a 500f oven and calling it done when it browns. I really have never taster a thing out of a stock popper that didn't taste thin and with very little flavor development and to say that city to city + coffee tastes that way is just BS. Different beans need different approaches to roast them proper and that takes some control over the roasting process to get heat to the center of the bean not just the outside.
I say roasting over an adjustable gas burner in a pan and stirring with a spoon or whisk can give a novice much more control over a roast and a better understanding of how simple changes can bring out the most from a particular bean. Not to say that this method doesn't have it's drawbacks since it is very easy to burn the outside of the bean especially on the flat spots. Peaberry beans are the best way to learn this method since they have less flat spots because they are more round.
Just my
.