There is an objective risk you'll be asked to check it in at least some of the time. Hand luggage policy tends to vary vastly across stations and with both AF and KL, whilst enforcement is not particularly strict at hubs IMHO, I have been to a number of outstations where it has been fierce. The bag you want to buy is very significantly above what is allowed on AF, KL and most European airlines so you simply cannot be guaranteed that you will always get away with it, nor, arguably, should you given hand luggage issues on so many AF-KL flights.