I don't really like crossdraw for a number of reasons. A forward cant with proper holster retention mechanisms and retention training would be plenty effective.
I like cross draw, especially when driving. It is sorta a necessity for me when carrying two OC revolvers. Plus cross draw makes a rear gun snatch difficult, add to that if a fixed blade is the backup, most sheaths are designed for right hand. I am stronger, and can stab much more efficiently with my strong hand, while my weak and and body position protects the gun.
As far as retention holsters, they only work if the crook does not know how they operate. If you are using a Serpa, or similar, most everybody knows how they work. Not to mention I do not put myself in those situations in the first place. IF someone is going to do a snatch they are most likely to do it from behind.
That said if I am not driving I usually carry strong side, and use my SA to guard against the unicorn gun snatch.