A recent Steam Controller update (possibly beta only update) added a second Bluetooth pairing slot, letting you pair two Bluetooth devices (just like how you can pair two pucks). To start the controller in the second Bluetooth slot, you turn the controller off, and then hold L1 + B + Steam to turn it back on (versus R1 + B + Steam for 1st BT slot, or R1/L1 + A + Steam for the two Puck slots).
That said, the main thing I wanted to talk about in this post is how happy I've been with my Steam Controller. I know it's been overshadowed by the Steam Machine/Steam Frame, and there's been supply issues/over priced, but it's been a really great controller for me. I find it fits my hands really well, and I've been playing my Steam Deck docked a lot more since getting it.
The magnetic puck for charging works great, it's been effortless to keep it fully charged between sessions. I've never really gotten to test the controller's supposedly great battery life because it's so convenient to charge. Having the track pass/gyro/back buttons has been great, I found myself missing them a lot when using other controllers. It's also great having a controller with track pads for times I need to reply to a steam message or type something in a game.
I haven't really used the grip sensors. I can imagine some uses for them in games where I want to use gyro without touching the thumbsticks/track pads, but realistically I haven't encountered a game where that applied. I could also imagine using them to pause a game when I set down my controller, but that's not really much of a need and I could imagine it backfiring. They're an interesting tech but less useful than the capacitive sticks imo.
A minor inconvenience is that the waking up the steam deck via the steam controller (through the puck) seems to only work if the steam deck was connected to the puck before going to sleep. To get around that, I've paired the controller to my deck via Bluetooth as well, so I can swap to Bluetooth to wake it up, and then swap back to using the puck for latency/etc.