A well adjusted shoulder holster can be comfortable. It takes a little getting used to. If you're going to conceal carry, then you really need a loose fitting jacket. It doesn't have to be baggy or over sized, just a little loose.
I don't ever recall hearing/reading a story where somebody got shot or an accidental discharge by a firearm that was being worn in a rear facing shoulder holster.
When I carry my .40, in the case that it came in, the muzzle faces forward or rearward, depending on which hand I carry it with. It's never once fired uncommanded.
Same thing, when you have your firearm in your car. Your muzzle is going to be facing somebody at some time. It can't be avoided. Felid`Maximus made a good point with being on the second floor.
Now, if my firearm is out of the holster, and my my finger is around or on the trigger, then the muzzle becomes an issue.