Tubeless5812
I wrote a long rambling post that I decided to summarise instead. I love that it's basically a PC laptop with all of the flexibility that comes with it, that's smaller, light and portable enough that I can I take everywhere.
But more importantly, it's gaming focused - the controls are great and it's fantastic for emulation and weird use cases, like running Interstate 76 with 3DFX support and the correct framerate.
I love that I can replace the hard drive or install whatever I want.
Not what you're asking for, but another option is to use a DualShock 4 controller which also supports touchpad (which can be divided in left/right if you want). I've found a pretty decent amount of community support and often use the touchpad (or gyro) for mouse games, though it's not quite as comfortable as the Steam Deck .
(I'm sure Dualsense 5 works just as well but I can only speak to Dualshock 4, which you can find for the cost of a HDMI cable online).