i needed a cheap rear mech for an old bike to convert to 1x10,
this derailleur is quality. No clutch mech button (aka shadow+) on it, but i've not been dropping the chain so no problem.
This is the SGS model (ie Long) so can be used with double and triple chainrings also.
Please note it is 10 speed, if you are upgrading from 8 or 9 speed you'll need a 10 speed cassette, chain and shifters
these are £33 on CRB/Wiggle and the Deore M615 is £36.99, so a very good saving.
Mine came in retail packaging, and not OEM