This type of minimal "holster" always worked fine with my appendix carry, in vehicle or not.
I'm not very heavy, appendix carry is fine with me, the Shield is very flat, the trigger guard cover stays solid and there is a zero
possibility to gets removed while I'm moving or something to interfere with the actual trigger, besides, coming from SA, usually 1911 type of pistols,
I'm used to take down the safety while drawing, so it is another safety measure if you will, my model does have safety, same cover for my G17, no issues...
It draws nicely out of it, close to the body, and your gun goes naturally in SUL (hard to describe otherwise) at your chest, and in low ready if you need to go further.
If I have to carry otherwise, I also think the 3-4 o-clock is the most fusible option, plus whoever train IDPA and such, should have the needed muscle memory in
order to draw fast and reliable.