I have the Roll Masters and they really worked good sliding a '40 Ford around the garage as a one man operation. The company was on my way home from work, so I saved on the shipping. I had the light weight versions, but my friend bought the heavier duty ones and they would move his '67 Cadillac easily.
I have a one set of the HF cheapies and they work ok. Seems like I use them more for rolling around transmissions and heavy parts. I just set up an account last week to sell the ones made by Merrick Machine in Nebraska. They have been calling me for a year trying to get me to become a dealer. I just listed them on my website. You can visit their site at http://www.merrickmachine.com. PM me, depending on the size they weigh between 50 and 85 lbs, so I doubt I can give free shipping but I'll help all I can.
I read somewhere that the main problem with the Harbor Freight version is the wheels' axle hole not being centered. It's a hit-n-miss thing with them. If the axle hole isn't centered, you're basically trying to push an egg. I haven't bought a set yet, but they're in my future. I'll probably just give all 16 wheels to a friend with a lathe and have him center/enlarge the holes a bit and see if I can buy some bronze bushings for them, with a hardened bolt axle. -Brad