I've been running these wheels for over a year. I have one pair of the 775 and one pair of the 778 (15QR front).
Pros:
Relatively light
Have needed little truing
Seal extremely well with UST tires - no sealant needed
Shimano tech support in US has been awesome
Cons:
Early freehub bodies had some durability issues
Freehub body bolt is prone to loosening - use some Loctite if it ever loosens up on you. Shimano may be adding Loctite at the factory on newer models
Supplied alloy spoke wrench will do more harm than good - source a Park or Shimano steel one if you ever need to true
Proprietary spokes/nipples are likely a special order item
For $400, I'd say go for it.
-D
Pros:
Relatively light
Have needed little truing
Seal extremely well with UST tires - no sealant needed
Shimano tech support in US has been awesome
Cons:
Early freehub bodies had some durability issues
Freehub body bolt is prone to loosening - use some Loctite if it ever loosens up on you. Shimano may be adding Loctite at the factory on newer models
Supplied alloy spoke wrench will do more harm than good - source a Park or Shimano steel one if you ever need to true
Proprietary spokes/nipples are likely a special order item
For $400, I'd say go for it.
-D