It's stable, works as good as my DualShock 4.
Though I used it very little over Bluetooth, I prefer the 2.4g dongle, so YMMV.
Edit: 8BitDo sells this controller in 2 variants: The Ultimate 2 Wireless (comes with the 2.4g dongle, Xbox button layout) and the Ultimate 2 Bluetooth (No dongle, Nintendo Switch button layout).
Maybe the Bluetooth variant works better?