I have used (on a NEX-3) its "little brother", the 500mm F/8 - well, under a different brand, but it's basically the same lens design made by Samyang and being sold under a dozen different brands for decades.
Most people would say that "cheap junk" is a more accurate description than "nice price point". The optical quality is adequate at most. Wide open, it's downright bad - and remember, wide open here already means F/8! And of course it's manual focus (and aperture).
Still, there are conditions where it will allow you to take shots that would otherwise require a lens that costs at least 10 times as much. If your camera has focus peaking (the ones you cite do, I think), your subject doesn't move and you have either direct sunlight or a decent tripod, then it can be useful.