The joystick quality is fine on the Legion. Similar to an X-Box Controller.
It’s got six different trigger buttons on the backside, and it is easy to accidentally bump some of them them while you’re handling the device, so keep that in mind when you’re mapping your button functions.
The controllers on mine are detachable, and the right side controller comes with a little base you can set it in and slide it around on the table to use it as a wireless optical mouse.
It comes in a nice padded case. It charges via USB-C, but you have to use one of the larger 65W chargers, and the charger doesn’t fit into the case.
It seems pretty solid and well built. It’s got fans and vents and ports all over, so definitely not as water resistant as a phone or tablet.
I’ve never used a Steam Deck, so I can’t compare the two. I’d recommend the Legion to pilot a BlueROV based on my experience.