We reviewed the Ratio Mech (£287.50) earlier this year. This modular, user-serviceable derailleur was designed from the ground up by the Ratio team in the Lake District, UK. For 1x drivetrains only, the Mech can be used with a wide range of cassette and shifter pairings. John gave it a complete rundown in his review, so if you missed that, check it out.
Just announced, the Mech is now available with a silver cage and hanger, to add a nice bit of bling to your build.
Check out more at Ratio.