Here’s my Poon tale:
I had a 10.5 degree M2 with a hzrdus yellow shaft which I hit great. I put the shaft into another M2 head but 9.5 degrees. Club was awful now for me. I put the shaft back in the 10.5 and it still didn’t work. I ended up selling both heads. Poon escaped because the shaft was completely separated from the head.
To replace the M2 I bought a Ping G400max 10.5 degree with a Graphite Design Tour Ad IZ6 shaft. I tried it at 9.5 and it didn’t work for me, I went back up to 10.5 and it was fine. No loss of poon because the shaft stayed in the adapter sleeve and was just rotated.