Open for iwb concealed. Strapped over the top for my ankle when I'm on my Harley...
Pretty much. If it's being carried open wether for duty or not, without added retention it's pretty easy for someone to take off of you. If it's concealed, no one should know it's there.
IMO a thumb break is too obvious when open carrying, but that really is just an opinion.
Off duty I open top carry in my Zero9 kydex holster. The "retention" is built in when the holster is molded, there is a very audible 'click' when holstering the gun. I'd have to hold the holster upside down and shake it pretty good to get the gun to come out.
But if someone was to make a grab for the gun it would come straight out right?
The retention in an open top Kydex holster is purely it clipped in around the trigger guard.
It does cover, just didn't seat it far enough for the pic..I do not know who made the bottom holster in the OP's picture, but it seems to me that not enough of the trigger guard is covered.
If you have to worry about your gun flopping out of an open top holster, your holster is poorly built.