I am sure these ditching courses are great (genuinely so - anybody thinking otherwise needs to try to get into a little rubber boat in a swimming pool to see that it needs a definite "technique", and that is in calm water...) but I think it is safer to fly with a raft without going on the course, than without a raft and having been on the course every 6 months.
But almost nobody flies with a raft, presumably because the £1000+ cost puts people off.
(I used to be asked by flying schools/clubs if they could borrow mine. I did it just once... having got it back opened and re-packed. Had to send it off for an overhaul after that.)