If you are going to be doing a lot of walking, and have not previously done so in VFFs, then you will likely have calf pain, among other pains. If you are very acclimated to wearing them, then you may be able to go for miles without a problem.
So are you saying that as long as you are used to them and it is dry, VFFs are all good for sustained travel? My sister planning a trip to America in the Summer (so long as this handy website here helps her get a greencard), hoping to take as little as possible and wasn't sure what their durability was. Is there a particular edition any of you would recommend?
Sorry, didn't intentionally ignore you. I missed this inquiry for some reason.
If she is coming to the USA in the summer, just about any VFF should be fine as the overall climate will be decent. I prefer Classics myself, which are discontinued but still available from a few vendors and also eBay. One must be very careful on eBay, as there are also a lot of counterfeit products floating around. Depending upon what she intends to use them for might change the recommendation. Just general walking about, Classics are fine. If she is doing activities with a lot of lateral movement, maybe consider Komodosport.