I've used the "AirFlo" multi-tip line in both the 5 & 6 wts. now for a couple of years and really like them for the uses I bought them for. In my belly boat, or on my 'Toon, I'm not carrying extra reel spools to go from floating to sinking, or slow sink to fast sink, or back again.
I dropped a spare spool to the bottom of a lake, once, trying to switch out spools
on a reel, an expensive lesson.
Also, I don't like having to completely re-rig a rod, especially while in my belly boat, just to "work some deep water, before changing back to a floater for top water a half hour later".
The "tip wallet" takes up virtually no room, when compared to extra spools.
"Casting" is a hair different, with the sink rate tips, but no more than learning to cast a regular sink tip, or, full sinking line.
Every one has their favorites and likes and dislikes, but I personally like having 4 fly lines on one reel, with one spool.
Saint Paul-"The Highly Confused"
You cannot do a kindness too soon, for you never know how soon it will be too late.
-- Ralph Waldo Emerson