I have no experience with Chaffhaye in particular, but I do with other brands of haylage (which is what it is -- a packaged commercial brand of ensiled [fermented] hay).
I am not aware of packaged haylage being deficient in indigestible fiber compared to regular hay -- it can perfectly well be fed as a total substitute for the normal pasture and/or hay ration, and often *is*.
Its main virtue IME is that it is of consistantly high quality (high nutrition, and not dusty or moldy). This makes it valuable in two general sorts of situations: if you have a horse that is very sensitive to dust or mold in normal hay, or if you have a lot of trouble obtaining a reliable supply of good-enough-for-your-particular-horse's-needs hay. It is also (less often) used for horses in serious training, or poor-keeping elderly horses, when you want to combine their necessary fiber ration with as much nutrition as possible, to get maximal effect from what you're putting into the horse.
Its main downside is that it is REAL expensive unless you are in a "decent hay is real expensive too and sometimes impossible to find" area. Also the bags ought to be used promptly and even so it isn't a bad idea to have the horse vaccinated for botulism (although that does not confer 100% protection). Also, it does not "agree with" certain horses, esp. some individuals prone to colic or laminitis. (I do not know any way to predict which horses will do well vs poorly on it though)
I would not use it, personally, unless I had a severe problem with getting consistantly-adequate hay. But if I did have that problem, I sure would go with haylage (preferably commercial bagged brands of haylage rather than 'homemade' bagged roundbales) if the alternative was grossly-inappropriate hay or none at all.
JMHO, good luck, have fun,
Pat