It's true if you have a urinary problem and lots of people do, this type of underwear can be very helpful because they are so easy to wash and so quick to dry and they can be thrown away at will if need be. I don't have that problem now but I did have in 2015 when I had my prostate removed because of Cancer. The Nurse said my incontinence would last for 10 days and the amazing thing was that it did. I didn't know about this Decathlon underwear then, if I had those 10 days would have been a lot easier to manage. Until 2015 I never gave underwear a thought, just popped into M & S and that was it, with an incontinence problem underwear becomes much more complicated, especially if you have to wear a catheter for a short while.
I do find however that in my case the underwear sizing is important for hiking/running comfort and effectiveness, I'm a medium, have a 32" waist and the choice for me is do I want an overall tight grip around my bum, hips, waist, and abdomen, or a less tight grip? Both sizes do grip me where they should and not where they shouldn't (the underwear is stretchy) but my choice is the 'L' versions, on me, they feel just right! I would even go so far to sometimes think, am I actually wearing any?