Phil,
I've used both the Harbor Freight manual dolly and an electric dolly. This was necessitated by the fact that we have less than 4" of clearance on either side between the TM and the gate posts on our fence. So while I can back the TM into the space, it's still too small for the tow vehicle to fit with mirrors out and as you know, backing a trailer without side mirrors is not happening. So I can only get it so far back and then need to unhitch and roll it.
We started out with the manual dolly (which I still have and if you're anywhere near Denver, I'll give it to you) but since I have a heart condition and a slight slope to the driveway, it was just too strenuous on hot days to feel safe. So we bought an electric dolly from
www.powermoverinc.net and are happy to have it as it makes the task quite easy.
Basically, if your driveway/garage is perfectly flat, you should get along fine with the cheapy. If you have even a slight slope, you might still get away with it, but you'll want to be careful and I would also recommend hanging on to your emergency brake cable. But if you have much of a slope, you might consider taking the load off and getting an electric dolly.
Power Mover and Power Caster are the only two brands I know of and I opted for the Power Mover because I felt like they had a bit better deal for the money but I'm sure they're both fine.
Good luck and watch your toes!