Summary: I have the T2i with the BG-E8 grip. It fits well and is comfortable. Attaching the strap to the camera is not intuitive, and it does not come with instructions. If you search the web, you will find a diagram showing the procedure.
Summary: The E1 Hand Strap is a good product but takes some getting used to. The added security is welcome when hand holding a $6000 pro body & lens. The biggest con is the set up, there are no instructions on how to correctly instal the strap and it is not intuitive if you want to do it correctly. I had to search the internet for a description on how to set the strap up so the regular neck strap could be used in conjunction.
Summary: Took about 15 minutes to install once I found the installation diagram online, and thats for someone who hates installing straps that have to be looped and threaded 20 times. make sure you take it "apart" before you start installation. it comes with a little plastic plate and a metal plate already with the strap threaded through them from Canon, but it needs to be disassembled prior to instation on your camera. Diagram online doesnt show that little detail.
Summary: Albeit pricy, this hand strap is a must have for photographers using cameras with battery packs/grips. It came with no instructions, however a quick trip to Google and searching for "E1 Hand Strap" then clicking the image tab brought up several sites with clear directions. You can use both this hand strap and your neck strap. There is a tang on it to thread your neck strap through. I would buy it again ...
Pros: Adjustable, Comfortable, Does not Chafe, Strong Construction
Summary: Back in the digital rebel days,when I got back to SLR cameras,I found myself,not using my neck strap,but holding the camera with my right hand, it just felt better walking that way. Tried the E1 hand strap and have never taken it off. I keep them on my 5D and 5D mk2, now with a fast remove neck strap,yes you can use both at the same time. The E1 is a easy install,nice leather and well padded.
Pros: Adjustable, Comfortable, Does not Chafe, Strong Construction, Well Padded, You'll never take it off