I glass bead a LOT of parts for restoration of vintage Mercedes Gullwings and Roadsters.
Line pressure is the key (as well as grit size/material of course). It's most noticeable with aluminum castings. ~ 40 psi seems to give a nice smooth satin-like look. 120 psi gives it a shot peened appearance (not bad in some cases, but NOT for a $1M investor car). At high pressure (over 100 psi) small parts, especially sheet metal will bend, warp and twist.
Also found that when polishing plastics/acrylics, a final pass with carnuba wax gives it a boost.
YMMV
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