Classic Kanken vs Doughnut Macaroon

I’ll be travelling with personal item only for 5 days, and the only backpacks I have are my work backpack (which is too small) and one of those viral Amazon travel backpacks (which is really bulky, and has for example a super padded laptop sleeve that adds bulk and that I won’t need for this trip).

I’m thinking of getting another bag for these short no-laptop trips, and one that I can also take with me while exploring during the day and for day trips (so it should look relatively nice). I have the chance of buying a second hand classic 16L Kanken for 15$, or a new Doughnut Macaroon for 50$ on sale. I know the Doughnut is more recommended here due to sturdier materials, more comfortable straps, etc. But is it worth the price difference in this case? How uncomfortable do the straps on the classic Kanken get? Does the Doughnut have more space/better use of space?

Thanks!!