I shoot a lot on the street with 5d3 and either 35l, 50l or 85l. I don't like to use my neck strap (or black rapid) because it attracts to much attention. I'm after a wrist or hand strap that is secure.
I use the Canon Hand Strap E2 on my 6D. It works great with the battery grip, which has a convenient strap lug on the right side, but can also connect to the tripod socket with the included nut or to a Kirk/RRS bracket with strap lug by removing the tripod connector.
There are also Chinese knock-offs from the usual suspects that are far cheaper, but it wasn't worth the risk to me. That's a lot of money riding on those stitches and buckles.
I use the Canon E1 hand strap. It's been replaced by the E2, slightly different shape but adds the tripod socket lug. As wsheldon points out, you don't have to use the included lug - RRS/Kirk plates and L-brackets have a lug.
I use the Camdapter Handstrap Pro on gripped 7D. Very convenient. I stays permanently on camera along with blackrapid RS-7 (attached with B2-FAB-F 38mm clamp to RRS L-Plate). I use only the hand grip if the camera is mostly in the shoulder bag, and pops for the photo.