Thanks Itc & Digitech for your quick responses. It's reassuring.
Fyi... I have the Tucano (60cc) from Phoenix, which btw flies really well, and its' 2nd have is supported by 3 tubes (at half the fuse X2, and lower part X1). The PC21 is only supported by one tube and 2 little guides just above (lower half of the fuse).

I must say the quality of wood and assembly seems great on the PC21. And although the servo mounts are of quality wood and glue, because of my Tucano, I did renforce them with fibreglass cloth and époxy (just personal insurance... for which your buddy should consider too during his Tucano build).