Once you actually travel like this a lot you come to realize that changing clothes is basically optional. And as far as value per kilogram goes, smartphones are pretty much impossible to beat (well, maybe certain categories of medicine if you have some kind of condition, but otherwise I can't think of anything)
Well, it gives them unlimited access to information, which helps a lot when arriving in a new city. The lack of a change of clothes is a bit gimmicky and relies presumably in being able to find a washer and drier pretty much anywhere.
You can find a washer and drier pretty much everywhere. Most hostels have facilities for washing clothes, and hotels usually provide this as a service. And then there are laundromats of course.
The only problem is what to wear while washing stuff, and of course the fact that you need to handle this quite often if you only travel with one set. This is why I always travel with one or two changes in my backpack.
I would absolutely do the same. Get one of the apps that downloads WikiVoyage and you have a detailed guidebook for all of Europe (including phrasebooks for every language) that doubles as a camera and flashlight and fits in your pocket.
From personal experience, you'll rather want one of those: https://en.wikipedia.org/wiki/Pareo , which is essentially a big thin cotton square.
It fullfills all the functions advertised for the towel, but is far better at the critical ones (for earth-confined travel), such as doubling as clothes and a scarf, and it's far better as a rope than a normal towel.
As someone that started traveling when good smartphones were in their infancy and I didn't have one. Just trying to pick which bus to take or how to find an information kiosk, you'll spend all day trying to figure either one of those things out.
