I recently did a p4.5-ish (knife edge but bordering on back of hand) rfid install, which wasn’t terrible pain-wise (I’ve done enough needle installs that I’m kind of used to it, but in comparative terms, more than a p0 but less than injecting lidocaine into a fingertip). However, the skin thickness is definitely a challenge, like people have said, and it’s a fine line between too deep and deep enough that it won’t get in the way in day-to-day life.
In terms of xG3 placement, I have a v2 in my forearm (anterior/radial, just proximal to/above where I wear a watch), which was a very easy install and is useful for lifting things, but doesn’t do much sensing.