The shoes were tested with elite runners on treadmills and based on HR lowers at the same pace they determined a savings of 4% energy output (vs previous shoe tech).
You can read elsewhere about the carbon fiber plate and fancy new foam tech that make these shoes so light (7.5oz) and springy.
The first Vaporfly's were impossible to find and super expensive. Lots of scammy looking deals on Amazon for big $$$. They also had a reputation of being really fragile and wearing out very quickly. I did not bite.
This is the second version of these shoes and so finally: I was able to find them (from Fleet Feet) for the Nike advertised retail price of $250. This is 2X+ my Kinvara 10's (~$110)...would it be worth it? At that price my plan was to use them for races only.
What's it like to run in them?
The second run was after a rest day: I was ready to hammer! I had not done a really hard run in quite a while and wanted to see what these shoes could do. I really got into them at the faster place and figured out how get a comfy stride.
Upshot: I ran 7.5 miles at 8:50 m/m pace, average HR 131 (my max HR ~160)
This is one of the fastest decent length runs I've had in quite a while at a sub-9 pace. In fact, I had to look back to 2013 to find a run with the similar pace and low 130's HR. 6 years at my age (63) means about a 6% slowdown....so it looked like for me the improvement was 6% rather than 4%. (This is not surprising to me, as some of the articles mentioned that for slower folks the benefits might be bigger.)
I ran 9 miles today, a hilly course so hard to compare, but boy did I feel great again!
I haven't seen anybody say this before (or didn't see it) but it came to me after my first run:
I can train harder because I can recover faster.
Getting a bump up in efficiency is great, but being able to train harder is also huge. At my age I find that doing hard days (intervals, tempo runs, etc) really beats my legs up from the pounding. This limits how much training I can do at higher heart rates.
The post run feel with these shoes is different: reduced soreness. The muscles have been used for propulsion, but not (as much) for shock absorption.
In another few months I will post again about this...stay tuned!