Agreed, think twice before you go for the sealed type. My last trailer had Alco sealed for life bearings. They were great in that you could forget about them till they needed re-placing. The trouble was that that was every 18 months and then you had to buy a complete hub at £100+ to replace them. They also give little warning when they are about to go, other than a grumbling noise. One tip though, the hub unit from Alco is the only official way you can buy them, but if they're the same as I had, they are actually an ordinary bearing as fitted to a Bedford van. If you can find a friendly metal worker with a press you can press them out and buy new ones from a motor factors for about £26. Can't remember what type they were but I did post that info last year here. Do a search for bearings and you may find it.
Interested in you comments about the bearing savers, Dave. My current trailer for my 6.3 is a single axel Rapide, rated at 1,800 kilo gross. As such it has a thicker than usual axel and thus needs a bigger than usual bearing saver. Difficult to get, but if they are as good as you say, it may be worth the investment. Why don't Bradley put grease nipples on their axels?
And waterproof grease! Try Aqualube!
There now follows a cacophony of nipple jokes!