Pop Down® Education
If you could easily remove a pop-up stopper, this is what you might see.
Rotting, noxious, unsanitary gunk: nasty.
The traditional pop-up drain is built to clog, by design. The "T" slots in the typical flange allow grime into the overflow. Just because it's "free" with a faucet doesn't mean you should recommend it.
Pop-up drains are unsanitary, difficult to clean and, most of the time, they don't work.
The solution to the pop-up issues are to disassemble the entire drain from below the sink and clean it –over and over, year after year.