A little more aggressive than the chiro that used a thumper device on my spine, but same basic practice.
The hand holding the block is actually buffering the blow pretty well, and he isn't exactly smacking that hammer full force.
I'd do it.
Anything that can be adjusted into alignment like this can makes its way out as well.
One might experience some relief (either real, or relieved that the procedure is complete.)
Eventually, things will be back to where they were prior to the visit if the cause is not addressed.