Ball bearing advice needed

Yes.

You might be surprised to hear that it may not make all that much difference. As you say, you might expect rubber seals to be better, but because of the limited space they are more flimsy than the separate, spring loaded lip seals that you will find on things like car drive shafts and gearboxes in general.

Shielded bearings are surprisingly good at keeping rubbish out unless aggressively splashed with water because they sit in a recess that retains a continous "bead" of grease, at least provided the bearing does not "dry out" because of excessive heat or very long service. Shielded bearings may have marginally less drag. Sealed bearings may have lower speed limits (on very high speed items) because of frictional heating, but you won't be anywhere near the limit on a mower.

In agricultural vehicles where the environment is typically very aggressive (not just the mud and water, but plant fibres getting wrapped around shafts, etc) there is usually an outer lip seal but also, very often, a fairly elaborate labyrinth type seal that is filled with grease between the bearing and the outside world.

I'd usually say go with manufacturer's recommendation unless there is a real supply problem. But in this case I would not lose sleep over it. You do want one or the other, though.

Hope that helps!

Many thanks for the detailed reply, based on which I'll stick with the ZZ version.

I'd have thought those might rot. You are lucky to have bearings! Sounds a bit like the start of a Monty Python sketch, When I were young it just had a spindle running in two holes laddie. Brian

Rubber seals on "everyday" bearings are likely to be nitrile, for resistance to the mineral oil in greases. It's slightly more weather resistant than the cheapest natural rubber or its synthetic equivalent. Not especially UV or ozone resistant but then not necessarily particularly exposed either.

Slightly but not all that much.

I thought nitrile handled heat better too?