so looks like for every 100 people joining the network, 5 are leaving
Not quite. @various_mm.
Annual churn is still a little over 50%. To put it another way, slightly over half the entire customer base leave the network each year.
There's little information from other similar, non-contract MVNOs concerning churn but, from what I've seen giffgaff have a somewhat above average churn rate and are markedly above the rates reported by networks offering long term contracts.
thank you for this info