I play both anchored and not depending on what I'm playing.
I also find anchoring my wrist to the bridge area and curling my fingers in helps with speed and less strain.
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This!
I can do both, but when I do anchor it is not as hard of an anchor as I have seen most do. My pinky rest on the body of the geetar but there is really not that much pressure.
There was a time when I tried to pick exactly like Gilbert but then I realized he is an alien so I just modified the way he holds is hand to work for me. It feels like I have more strain on my hand when I try to keep my fingers curled in, so I just let them relax and it is way more comfortable.