Pressing the clock with a captured piece

Bad manners or just abusive?

....or ergonomic ?

The hand makes one longer continuous movement instead of two shorter ones longer in overall length...

Neither?

You have to use the same hand that made the move, anyway.

joke on them when the clock is triggered by touch heat and using the piece doesn't work xD

I'd probably say not a huge deal, but maybe not good for the pieces based on how hard they hit the clock. If holding a captured piece, I usually just hit the clock with the back of my hand by tilting my wrist a little.

It's not that hard to capture a piece, put it down next to the board, then press the timer (unless you're playing blitz or bullet).

That's why I don't like to use my "good" chess set for speed games. Who knows how the opponent will handle them...I've seen players knocking over pieces, slamming them, and generally doing everything they can to not lose seconds on the clock.

If it's my equipment, I won't allow it. If it's the other guy's equipment, I don't care if he does it...

6.2.3
A player must press his clock with the same hand with which he made his move. It is forbidden for a player to keep his finger on the clock or to ‘hover’ over it.
6.2.4
The players must handle the chessclock properly. It is forbidden to press it forcibly, to pick it up, to press the clock before moving or to knock it over. Improper clock handling shall be penalised in accordance with Article 12.9.

https://handbook.fide.com/chapter/E012018 

It's your chess tickling captain here. Pressing the clock with a captured piece saves time and energy and furthermore, let's the piece do some overtime work after it's left the game.