Running

Using runrepeat listings, your flyknit racers are 130g lighter than the speedcross. A very different trainer.

As @Sainsburys_Ed mentions they're good hikers too, I also wear mine for gardening too & also long stints on feet on a hard (painted concrete) surface at work on which road shoes quickly give me sore feet. I do run in them too still.

If you want a really light but grippy trail shoe it may be worth a look at the inov8 x-talon 212, as name suggests 212g. They'll wear out quicker on harder surfaces though if owt like my 190's (my xc shoe past 2 seasons, sadly discontinued).