I've been around guns for approx 25 years. As a armed professional, US military service member & armed citizen, I can honestly tell you that straps or retention systems have merit for sidearms.
Open top styles can do well for strong side concealed carry but I'd get a level II or retention type rig for everything else.
I've had 3 incidents where a firearm slid out or came out of a holster. There were no ADs or problems but my weapons got nicked up.
Use common sense & good judgement.