Benefits in upgraded pulleys

It's not smoke. Those are very pretty anodized gems that make you smile even though you can't see them while you ride. Personally I've never FELT any difference. But I'm sure the companies will tell you there some percentage more efficient and that their very pretty. I'd say, if you approach your bike as art, go for it. If your bike is a tool for fitness or fun, save the money for your next set of tires.

weirdly ive had a few bikes where the pulleys have broken, some smashed to bits. Ive then upgraded the plastic ones to metal ones. No doubt being stronger they are less likely to fail - Ive never had any fail yet (not that that is conclusive at all).

I heard the more teeth it has, the more efficient it is, or something.

The more teeth it has the longer it will last as the friction forces are applied less frequently.

If youve ever pulled apart the regular plastic jockey wheels on a lower end deraillure you will see that it's just an axle with a metal " bushing." Tons of grit gets in there and you will feel a significant amount of friction as it gets dirtier.

The plastic wheels also develop slight play from wear and that can affect the "solid" feel of the drivetrain.

Most of the anodized aftermarket wheels I have seen use cartridge bearings. They should be smoother for the left of the wheel. No word on servicing them though as I haven't done that yet.

The more teeth it has, the less the chain has to pivot around its pins to wrap around it, therefore less friction (and a longer lasting chain).