They are a little floppier than rubber hoses. Definitely more bendy, which mostly is good, but occasionally there is a momentary flash of annoyance. For the most part, though, they're 100% fantastic throughout the dive. Zero reg pull. Really amazing, especially for the backup, but also for the long hose. Also, for the BC/wing inflator... you know how there is often that little loop at the back where the rubber hose is bent a little sharply before going into the first stage? No problem with Miflex. Packing is a DREAM. They're noticeably lighter, and curl up really well into the reg bag.
The only downside I see is a smidge more money (a small smidge, especially if you're comparing to Halcyon rubber hoses), and I've read one (1) report of someone here on the board that really didn't like the long hose for scootering, because it "flapped" in the "breeze". For the rest of us kick divers, that's a non-issue. And for other scooter divers who have reported, it's a non-issue. But there you go.
I love the Miflex rig on my singles rig (Atomic M1). All Miflex (except HP hose, of course). My double rig (ScubaPro Mk25/S600) is still all rubber, because I'm not dying to spend more money and there's nothing wrong with the hoses I have. I'll probably migrate the doubles rig at some point, though, and I doubt I'll be buying many more rubber hoses in the future. Oh, they're also really nice on deco bottles. You do have to be a little more careful holding them in place under the bands, because they're more slippery, but they loop over the neck very nicely, in use.