Update - both bikes sold and fatty acquired, in the end I plumped for the On One Fatty Trail - reasoning being as this was going to be my one and only bike, I wanted a bit of a do it all - and boy, does this bike do it all!
All my preconceived ideas blown away in 4 rides so far - this thing climbs, where before I'd be doing the old 'slip/grip' on the Chief or Bird, now the same loose, gravelly, steep climbs that defeated me before I just stamp down and it pulls me up like an E-bike. It's not as quick obviously, but with the trail designed geom, it makes a bloody good job on singletrack too! I have never smiled so much on a bike in my life. Don't regret selling the other 2 one bit! And all for just over 1k!! well done On One - what a bike.
Anyway, couple of pics, I've added a Hope seat clamp with the integrated dropper cable tidy and today swapped the black rim tape for Surly clown shoe orange - very pleased how it looks as well as it rides.
