I put this on my 2001 CR250 after I reliezed my stock one was all bent and beat up. The price on this guide was well below an OEM replacement and it's anodized. It bolted all up and installation was a breeze. I have about 10 hours on the bike so far and it is holding up great.
It's not a bad product once you figure out what it is. It doesn't come with any insructions on how to put it together so just look at the picture and you can figure it out. Seems to be a pretty good product haven't gottent to test it yet but it seems like it will be a pretty good product.
Unfortunately I have not used this chain guide with a sprocket that large. With that said, typically with a sprocket that large you will run into additonal wear and tear on the chain guide (if it even fits). You may want to consider removing an additional tooth from the front sprocket and running a smaller rear such as 52 tooth to guarantee fitment and prevent the extra wear caused by running a rear sprocket that large.