How long does the battery last on a charge?

The rated battery life is 180 minutes of cordless use. That is roughly double what many basic cordless trimmers offer, so most users can go weeks between charges.

Does it work on thick beards?

It is a two-speed home trimmer, so it handles short to medium beards well. On dense, long growth it will slow down more than a stronger barber-style clipper.

Can I use it in the shower or rinse it under water?

No waterproof rating is stated, so keep it away from water and clean the blades with the brush instead of rinsing.

What is the display for?

The display shows charge status and the selected speed, so you can see remaining battery before a trim.

Is it good for cutting head hair too?

It is listed for hair trimming as well as beards, but it is best for necklines and short cuts. For full haircuts, a dedicated clipper with more guards is a better fit.