> Has anyone ever fitted a Crew Saver mast float?
Yes; very strongly recommended.
The 9-litre float is not sufficient to fully prevent inversion, but it is ample to buy time – in which the competent helmsman and crew can take the necessary steps to right the boat.
Do not leave it up permanently; if you do, it will chafe badly, and within a season will become porous. Instead fit it on a halliard, and take it down each time you put the boat to bed. I learned the hard way; my first one was left up permanently, and did not last a full season, but the second one – which I took down at the end of each sail – is still going strong over a dozen years later.
Ideally use a halliard system which also keeps it tucked tight in to the mast at both top and bottom. One well-tried method of doing this is shown in the paper “Suitability for Cruising & Singlehanding”, somewhere around page 6, and this should be on this website. Unfortunately that page currently seems to be down. I will try to get it sorted, but in the meantime if you like to email me (cruising@gp14.org) I can let you have an original.
Hope this helps,
Oliver