Before my state governor signed the new 2A-gun laws, a county sheriff testified to the elected officials that armed citizens should be required to have level II/III type holsters and mandated retention skill training.
This requirements were NOT added to the final law. I also question how or who would pay for the required training or who'd enforce the new laws.
As posted, open carry does require being more alert & ready to fend off a snatch. With holsters you must address points like speed(open type holsters) and security(retention, SERPA or SFS, etc). I used to think the open style holsters were best for both open and concealed use but as times changed, I can see the value of some designs like the Blackhawk SERPA & Safariland ALS or SFS. They are fast, secure and able to be modified quickly(FBI cant, crossdraw, standard).
Why some firearm ranges or LE training centers would ban the SERPA holsters is what I don't get. I bought a M&P SERPA holster last Dec and it works fine. Even upside down the M&P was fully secure. You can't ask for more than that,
. I'd add that I wouldn't carry the SERPA holster in a rough or harsh climate(like SW Asia or the North Pole) but for regular wear or urban use, it's A-OK.