I Have a Donner Harmonic Square Octaver which goes up and down and also have octave divisions i.e 2nd 3rd 4th fifth etc and it works OK and is relatively cheap. I don't think any of them perform perfectly and I was reluctant to spend loads of dosh just to discover a minute differences in performance. I am putting a new topic on here for anyone using the TC Electronic Sub N Up(Quite like TC stuff) either standard or mini octaves, and more importantly using the Toneprint app to set user patches. Tempted to dry the Behringer for fun though.