I built my 54mm Tomach with slotted airframe. No problems to Mach 1.8. Build thread (including my rationale on the build I think) here:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4758
No problems with any paint or fillets cracking.
I have also done the half-scale Apache using a similar method. If I can get to a launch that isn't cancelled due to weather I might even get to fly it. Build thread here:
https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019&start=30
One thing I should mention is that my airframes (tail end anyway) do not take any thrust. I use the front of the motor casing to couple to an Aeropack minimum diameter style motor mount. "Thrust ring" does not contact the airframe. Tailcan stays in tension. This is not an insignificant difference in having to rely on the integrity of the tube.