okay...
First of all, the remote stop button on the left hood is right where your hand will go when you stand. It is far too easy to shut off your computer and lose miles off your reading before you catch it. Secondly, the gear readout often fails to trigger when you shift, giving you wrong info. The little chainring icon that is supposed to give you a quick view of what gear you're in would often freeze and fail to respond to gear changes. The lack of an auto-start feature is a minor annoyance, but puzzling in a top-of-the-line computer. NEVER were all the features working at the sime time. Programming the unit is complex and confusing, and the supplied manual is less than helpful. The virtual cadence was nice, give Shimano credit there. But even that is worthless if your gear indication is off! There are actually too many functions and they are too difficult to access while riding...especially in a paceline or other situation where concentration is required.
I know of others who have similar problems with Flightdeck, but in fairness, perhaps Shimano has improved the latest versions. Maybe others who have used Flightdeck can chime in.