there are lots potential problems with the casters. they are cheap, so they may, or may not [which is usually the case] roll freely. this can be caused by the casting process making the wheel diameter off center from the axle bore center [and it doesn't take much !], flat spots on the axle, burrs in the axle bore, or other items, bad bearing races, bad bearings, and on and on.
the other potential problem is the tire plates are thin, so when weight is added, the plates flex, causing the casters to go off axis, jamming up.

grease may or may not help. light weight vehicles, or ones without engines may not have problems using the cheapies.
when a guy buys the cheapies, then replaces the casters with good ones, you will wonder why you spent the money on good casters when the upgraded [pay more up front] ones are less money than you pay for good casters.

or fab your own. biggrin

anyway, that's my opinion. your mileage WILL vary.............
beer