Are they really worth having or are you better off just to have the hub cover and check the bearings visually?

read the post on bearing buddies. they maintain 3lbs of pressure on your bearings so they dont draw moisture when your hot bearings hit the cold water.

Thanks HD,  I had read that and I guess it's still a good idea to do a visual at least each season.  Nice to keep the water out while using the trailer.  I just hate to trust something mechanical to make sure the bearings are greased.  I've got old ones and I think I'll replace them.