Anyone hear of the Bower SLY30063CM 300mm f/6.3 Lens for Canon M EF-M

I googled and did not find much. They are acvailable on Amazon but no reviews have been posted

It's a mirror lens. Won't be very good optically, and have that ugly donut bokeh. If you want to try out a mirror lens, go to ebay and search for one you can adapt- you probably won't have to pay more than $25.
http://en.wikipedia.or​g …aphic_catadiopt​ric_lenses

http://www.bhphotovide​o.com …_3_telephoto_di​gital.html

Search instead for Samyang or Rokinon, you will find more hits under these brand names.
Also, don't look specifically for the EF-M mount, but you will find stuff on the other mounts it is available in

eg
http://www.thephoblogr​apher.com …or-sony-nex/#.VEFDgRbziDw

Lots of these and also 500mm f/8 versions. They are often fitted with an interchangeable T mount, so can be used on just about any camera body you like. Another thing you have to remember is that it is a fixed f/6.3 (or f/8 in the case of the 500mm versions). I have one of the 500mm lenses, which is branded Centon, which I believe was used by Jessops as an own brand.

It has very low contrast, although if you shoot RAW that can be fixed in post to some extent. IQ is generally poor, and you really don't want any sort of background detail, as the donuts are pretty unpleasant. I sometimes use it for aviation subjects where the background is the sky, so no bokeh problems, but they are still pretty poor images really. probably better on an old 6 Mpix body rather than anything better.

Alan