This is great. It is very simple to use, just clip it onto the headset support arm and plug it in the power socket. It’s quite small and not heavy; I didn’t notice the difference between when I used it and when I didn’t. I didn’t have any problem with it moving on my Quest 2 headset.
It charges quite quickly, a little over 2 hours, and when fully charged it more than doubled my play time and will charge the headset up to 100% if you use it as a power-bank.
I agree with other reviewers that it is a little naughty of the seller to advertise the power rating in mWh rather than mAh as is usual for power banks, but that doesn’t worry me. The test is how long it extends my play time and it wins on that imho.
I really like it as I can play a lot longer and don’t have to attach a long USB cable + charger into it.