Agree with TrT. Look for a school who has at least 3 or more serviceable helicopters online every day. A CFI with loads of hours plus at least 1 x Gr II instructor.
Also maybe look for a school where the GF area is close to the airfield. You don't want to spend half your time ferrying to and from the GF area.
Wonderboom in Pretoria is quite ideal. Once across the active 29/11 its 2 minutes and you're in the GF.