I've seen much slower ex-pat runners putting out 10 minute miles in Vaporflys and Alphaflys in Shibuya/Omotesando. Not really sure what it is doing for them at that pace/effort.
You can get them for harder efforts though, like long runs with marathon pace mixed in, long intervals, etc. If you can afford them, they seem to baby your legs for the next run. But you can always use them for races and after 100/200 miles turn them into long run shoes.
I'd say about 10% of the ~300 runners at the monthly race I went to on Sunday had them on (well 4%, Next%, some Next% 2, and Alphaflys). There were a ton of Zoomflys and Tempo shoes too... They weren't just the top finishers either...