Does anyone have experience with AC Delco 34646 Wheel Dollies?

http://www.oreillyauto.com/site/c/de...2121&ppt=C0192

Strength and easy to roll are my highest priorities.
They are rated 2000 lbs each so should be sturdy enough for my 4150 lb Roadmaster. They have 3" steel wheels (with no tire) and are supposed to be ball bearings but no grease zerks.
1) If you have tried these are they easy to roll around with a heavy vehicle on them?
2) Many of the more expensive wheel dollies have polymer wheels. Is this important to the wheels being easy to roll?
3) Will steel wheels mark up the floor? It is not painted.
Thanks