Can’t give you any feedback on the cotic but have had a Bird Zero 29 for a nearly a year now. Fairly modest build with some 35mm 140mm revelations, 1×11 GX and some old xt brakes I had. Because I wanted to run 2.6 tyres I did get some 35mm spank rims which are great.
Everything about the process with Bird was brilliant, from demo to purchase (frame only in the end). Ben was super helpful and answered loads of questions and gave me lots of geometry advice. I had a small issue with the rear axle on delivery and it was sorted within 48 hours.
I use this bike all the time from family xc rides with my daughter, mucking about, longer rides and trail centre trips.
It is so capable there have been a couple of times I’ve taken it to Cwmcarn and Afan in favour of my full suss to ride the DH and Enduro trails just see how it copes, and it does brilliantly.
Through the winter I used a 2.4 DHR / 2.5 shorty which worked really well. The rest of the year a 2.5 aggressor / 2.6 DHF. Not had any issues with comfort and would happily do longer rides on it.
Short answer, cant recommend it highly enough!