Didn't vote either due to complexity of issue.
Personally, I use a thumb break for concealment on my outside the waistband holster which is probably not necessary as long as the owb holster is well molded to the pistol. Alot of good holster makers do just this. Your average person will not be running, jumping, and chasing suspects so I think the well molded, no retention is adequate. However, since I am LEO and carry both concealed and openly at times (primarly plain clothes assignment), I need to have one system to remember when it comes time to draw. For my situation, the best compromise is the Level I retention (thumb break). The main reason for the thumbreak for me is to ensure that it doesn't slip out some how if I am ever in the prone or in a bent down position. Mine are also well molded so it would be unlikely but I do like it just in case. Additionally, I think nothing of popping the thumb break open if I am moving through a higher risk area such as a parking lot after dark. The thumb naturally goes where it is supposed to anyway.
Any higher retention over level I for a concealment gun I think might be overkill. However, to each his own.