My personal opinion FWIW:
The iRoast is a waste of money. It is not very durable.
The Fresh Roast 8 is useful if you have the ability to modify it and you also have a Variac. You can roast a 65g sample and control the profile that way. Unmodified, a FR+8 roasts too fast, but you can extend the roast time to 9-12 minutes with a variac. The main problem is that you really need to cool the thing down between batches. That seems to be the best way to do really small batches. I have 2 of them (used to have 4 but gave a couple away) which allows me to switch back and forth. I can roast 5 samples an hour easily using two of them. This comes in handy when I have 15-30 samples for an auction, and I am left with plenty of beans to go back and reroast darker or lighter on the ones that are really interesting or questionable.
Another method I have used in the past is a TurboCrazy, and I will quickly scoop out beans as the roast progresses (kind of a PITA). I have a bent metal spatula so that I can quickly scoop out 75g of beans an leave the thing running. It is pretty simple to get three roast levels out of an 8oz batch that way, and still have 8oz out of a 1# sample to try a different ramp. I wouldn't recommend roasting less than 8oz, though.
A good popper is an excellent method for small samples as well. If you can get a Poppery I you are golden.