Definitely a must! Clés are definitely my LV weakness. I have several. I use a clés every single day, they're great for attaching your car key, or for grabbing if you only need a couple of cards and some cash. I use mine for coins since I don't use the coin compartment in my wallet, I use them sometimes to hold earphones, and my USB flash drives. They're so handy!
I was just about to reply with an "ugh I never use my cles how is everybody making theirs work" but you (and this thread in general) have given me some ideas. Thank you!