I've used a few of Canon's tripod lens mounts on rental lenses. This is a solid piece of metal and seems to be built sturdy. It has a safety feature to allow you to rotate your lens without the clasp coming undone. It has a felt/velvet-like liner that has kept my lens barrel from scratches. I only wish it came with markings to indicate when it is perfectly vertical/horizontal. But the Canon 70-200mm f4 non-IS does not have this marking on it either. A quick fix with a sharpie (you can clean Sharpie with GooGone if you go to sell your lens).

Updated review. 11-2017

The top positive reviews are from 5-6 years ago, so maybe something has changed with their production quality since then, as mine is not as good. I initially bought this because it had great review scores, but I would not recommend it at all. I've even tried two copies and both had the same issues.

I have since gone back to the OEM version which works flawlessly with my Canon 70-200 F4 L IS. I hate paying so much money for something like this, but considering it is holding several thousand dollars worth of gear at times, it's worth it. Very precise, and it holds the lens steady without damaging the paint.

I have owned two copies of the Photodiox Pro and both of them had massive amount of play in the collar when tightened down. Since the quick release knob only goes 180 degrees, there is no way to make it tighter on my lens by twisting it more. It only goes so far. The two issues causing this are the loose hinge and the thin felt that is lined on the inside. If I tighten it down to max, the lens can sit statically without moving, but any amount of touching the camera when mounted can easily rotate it inside the collar. It would also allow for camera wobble in the wind when taking shots at 200mm on my tripod which isn't acceptable.

I ended up having to add some of my own material to the inside area of the collar to allow it to clamp down tightly. On top of the poor fitment, it was also causing some rubbing damage to the lens due to the lack of felt. If you shoot like I do and need to switch from portrait to landscape orientation back and forth often, this could be an issue.

Maybe I just have bad luck with a bad batch of these, or I somehow got some knockoff items that are not legitimate goods. I've owned other Photodiox products that worked fine. I also think some people may not realize how bad this item functions if they never owned the Canon OEM version which is a very finely crafted piece of gear. I'm always willing to try the cheaper products, and they sometimes work just as well as the expensive OEM version, but not this time.

This product is a fantastic value considering the Canon equivalent is $145. The build quality is very good, although the finish is not quite up to Canon 'L' standards. It is all metal construction. The inner felt lining is a little thin but does the intended job nicely (hold the lens firmly and does not scratch it). The locking mechanism works smoothly and very effectively -- I am using it with my new Canon 70-200mm f/4 'L' IS USM lens. As others have mentioned, I also had problems with the tripod insert...it would not properly thread into any of my accessories. I had to take a standard 1/4-20 bolt and run it through the insert several times to "re-tap" the threads of the insert. Hint: Start the screw in from the top side of the insert so that the first threads catch and then it will clean up the rest of the way. This makes the product work perfectly and I am very happy with the results...it threads into all my standard accessories now. Overall, I really like this product, I would have given it 5 stars if it were not for the silly threading problem.

Original one star review:
I bought this based on the price point and the mostly solid reviews. I didn't attempt to use it until after Amazon's return policy had expired (a big mistake, one that I won't repeat, ever). When I tried to attach a quick-release plate to it, I could not get the tripod screw to go into the tripod collar. Eventually, I determined that the threads on the collar were mounted upside down.

According to the product page, Fotodiox offers a 2 year manufacturer warranty, so I'm going to see about getting a replacement. The collar is snug when placed on my lens, and the closure is solid. I have no reservations about trusting my camera/lens to this tripod collar, once I get a usable version.

I'll update the stars and the review once I get a usable model.

Update:
Once I found the fotodiox contact information, they were very easy to work with (finding that information was pretty hard though, and the response times were a bit slower than I would have liked, but well within the time period they promised). They shipped me a new threaded portion, which I was able to install myself with a standard screwdriver. Product works excellently, and I have no issues, reservations, or misgivings about entrusting my gear to this piece of metal.

I bought this for a Canon 70-200 f/4 lens I bought used. After using longer lenses before with a collar I knew I wanted one. The design of this collar is nearly perfect and much better than the canon stock one at a fraction of the price. First of all the thing is solid metal yet not super heavy. The finish is great with no hard edges and matches the lens nearly perfectly in off white color. I love the operation of the thumb screw, a quarter twist and the lens is loose enough to rotate the camera 90 degrees into portrait mode, twist again to lock. If you forget to lock the knob tight thats ok because the collar doesn't swing open unless you also pull the knob outward. I also like the fact that the foot has a separate brushing for the 1/4" 20 threaded mount which means it can be made out of a much harder material or replaced if stripped. Since the threaded mount goes through both sides of the foot you can attach other things to the "top" side of the foot like a flash arm etc if you want to get creative. The only thing I would change about this collar is to build in a Arca-swiss style mounting groves into the side to save the hassle of attaching an additional plate to this collar.