We polymer clayers use toaster ovens to cure polymer clay so I'm familiar with buying them, and I've also purchased a few for food only.
The bottom line is that these days none of the toaster ovens are very good (even the expensive models often have hot spots, and some of the really cheap models can be fine...it's a total crap shoot). There are so many models too that it's almost impossible to buy the same one your friend has that works well, but go for it if you know of one that is already working well.
The main differences (besides cost) usually have to do with their size, number of racks, digital or analog, color, style, etc. So you should know what size you need first and buy for that, plus cost.
If you don't really need a large one, I'd suggest not buying that size because for toast/etc it'll just take longer to warm up and do the toasting.
If you really want to be "cooking" foods in it, I'd say go for a larger unit so that any hot spots will even out more in the larger cavity.
As for the "convection" thing, in toaster ovens that just means that a fan will be blowing the air around which has been created by the heating coils. The convection feature in toaster ovens doesn't seem to last too long in my experience but it's a good feature if it works though can be noisy (...and it's especially a good feature in a microwave-convection combo unit--see below--because in those there aren't any exposed coils and the convection works a long time).
Actually, this kind of "convection" is really *forced-air* convection, but plain old "convection" is a lot more than that.
Since toaster ovens are notoriously bad and when curing polymer clay things like hot spots, etc, can be reeeally important, it's often advised just to buy one, take it home, and test it... then be prepared to take it back (tell them it the hot spots are too bad, etc) and try another one. Some places will let you go in the back and plug them in before buying.
One way to test them for hot spots is to put 4-6 pieces of white bread on the main rack, then turn on. You'll easily be able to see how the darkness of the toast changes all across the field of cooking.
(Always preheat, of course.)
For regular cooking, you may also want to use a cheapie oven thermometer (where the food will be) to see how close that particular toaster oven gets to the temp you've actually set on the dial, and you can see how much the temps jump up and down as the thermostat cycles on and off.
Keep in mind though that even the tallest ones will probably put a whole chicken too close to the upper coils so you can put a sheet of aluminum foil on it to help deflect some of the direct heat or you can "spatchcock" the chicken and lay it down flattened instead.
If you can afford it, I'd suggest getting a *better* forced-air convection oven which would be the kind I mentioned above--a combination microwave and convection oven (not a "toaster oven" with a convection feature). You can use those only on convection or only on microwave, or a combination of both, and they tend to have pretty large cavities. There will also be no exposed coils in those so the heat will be more even for that reason too. They cook as well or better than regular ovens but will still be a countertop unit.
(There are other new countertop "ovens" too that you might want to look into if regular cooking/baking will be the main focus, but I don't know too much about those... NuWave?, etc.)
HTH, and good luck!