I used the Blackhawk drop leg hrig for when I had to carry around my infant son a lot. For me, it made carrying my son around much easier and comfortable than when I wore my hip holsters.
Now that he's over 1 year old, I don't have to carry him as much so I'm back to a hip holster.
I do miss how great it was to carry in the car with a drop leg rig. It was much easier draw while sitting down with a seat belt on. I try to carry cross-draw in the car now, but I end up taking my holster off, with the gun in it, and placing it somewhere accessible and secure.
Now that my wife is pregnant again, she'll probably be switching from a hip holster to a shoulder or drop leg rig. She told me that Hip holsters aren't that comfy when you have an extra person inside you.