How good are twist sockets?
 

I've got a glow plug that won't come out. It's rounded off. Tried a flank socket by Snap-on that is supposed to catch the flat sides instead of the corners and it didn't work either. My next attempt will likely be with one of the twist sockets like those shown here - http://buy1.snapon.com/catalog/pro_det.asp?search=true&item_ID=67377&PartNo=105TSTSMYA&group_id=17456&supersede=&store=snapon-store&tool=all. Before I spring for one or the set, do they work as advertised? Any other ideas also welcomed.

Len
'99 E300TD 71,500 miles

It works or it goes back!! the ad says, "up to 19mm but the sockets listed in the kit don't go up to 19mm.