Well many good bowlers love them and use.

Never did.  Always had a fast thumb release and clean.
All of a sudden this year my vinyl inserts have not been great for me.  Lots of humidity and lots of hang on the side of my thumb with last years size insert(and I've lost weight but seem to have a thumb looking like maybe ever so slightly wider!).

Finally a few things happened, picked up an old AMF Fit ball.  Old timey the ones that rotate top and bottom half, no adjustable pitches!  Some discoveries, very comfortable with my span fit with a slight tweak to it.  Got my exact thumb width which differs from the numbers on my inserts.....a little wider than I realized.  This itself is very important I am finding.

Finally put some Urethane inserts in with that exact width in(I have a quite oval thumb like many!)  I prefer to make the hole oval with tape or other devices.  I Had tried custom drilled urethane oval holes in the past, hated em.  And I have never enjoyed oval inserts.

I am seeing some immediate results.  First no hanging on the side, my arm was being pulled in front of me, my arm was being pulled away from my ankle, my hand ended up facing almost down on some of these hangs with my old and lately too narrow vinyl.     Almost completely gone! 
I will update as I try several tweaks!

Thanks Urethane, Thanks old timey AMF fit ball!


Regards,

Luckylefty
PS I love on my old timey AMF fit ball that round feel under my hand that I never ever got from even the AMF adjustable ball as fitters always had the piece for under the hand not in place!
http://www.ebay.com/itm/141066000232?ssPageName=STRK:MEWAX:VRI&_trksid=p3984.m1438.l2661