The j-clips work OK. I ran one in the back with a normal one up front. The problem is when the belt is slack (going to the bathroom) the C and J clips release from the belt. The standard clips stay put. The other option is the V clips if you have a velcro lined belt (ordered mine from the beltman, great belt) those would conceal the best and stay put, but you can't really adjust them without loosening the belt.
I used the J clip on the back, but switched back to the standards. I have the V clips on the way. I'll probably run one in the back and a standard up front, maybe both, I haven't decided.
As for people noticing, people are notorious for NOT seeing the forrest for the trees. Most are oblivious to everything, seeing a black plastic clip would mean nothing. IMHO of course.
CompTac CTAC for me, obviously, HK USPc .45.
Also, I used my dremel and trimmed off the rear clip down the the hole I was using. I noticed that the bottom of the clip under the screw would poke out a bit. I didn't like it, so I cut it off. I run the top hole on the rear clip, like the picture above, so I just trimmed the rest off.