Anybody has any experience with these idlers? Do they work better? Do they stay cleaner? Do need less grease?

The answer to all your questions is 'no'. Here are the problems witht hem, to the point where I no longer stock them:

1) Under stress- for example if you misshift- they tend to crack at one of the spiders which ultimately results in failure. This is not a good thing if you are far away from home;

2) They tend to wear the rollers on the chain faster especially if you have light alloy or plastic in your chain;

3) They don't fit perfectly. There is no "wobble" to them like plastic pulleys so gear adjustment becomes hyper critical.

I have a couple of handfuls of broken/removed units that the customers rejected.

The best way to keep the Jockey wheels clean is to put some solvent on a rag and wipe the chain down after a ride. I put a little charcoal starter fluid on a rag and wipe it down. If the build up gets too bad it's time to remove clean and re grease. Save your money and upgrade to another derailleur.