Is Ceramic Oversized Pulley really helpful?

Hi. Still learning. 

What's the deal with these ceramic oversized pulley? Is it really helping you or just aesthetics? 

Thanks.  - If yes, planning to buy one. Any recommendations?

Both the size of the pulley and the ceramic bearings are supposed to reduce the drag in your drivetrain.

However, I would not recommend spending your hard-earned money on one, as

1) we're talking very marginal gains for a high price which almost noone really *needs*, and

2) it's probably wise to prioritize durability in your drivetrain components if you are riding offroad (which I assume you do, this being an mtb website and all). This gets even more important if you ride in a wet climate or have particularly abrasive dirt, or if you aren't religious about drivetrain maintenance and cleaning (which would negate those small gains ten times over anyway).

In conclusion, don't bother.

Agreed with above. Unless you track wattage and are looking to squeeze out a fraction of a second on a long road ride I don’t think there is a marked value in purchasing those. 

Leave it for the Lycra crowd.