Great idea - so simple.
Good to see their Kickstarter campaign (which has almost finished, if you're interested) has reached it's goal - so this is going to be made.
I'd love to see different designs, and hopefully a children's version too (could be a double wrap around their smaller wrist). If they can/do look at producing these for kids, I think they'd have a much wider audience.
I rarely use a straw (even before I was conscious of the problem plastic straws were creating), but my daughter uses one almost every time we eat out.
And by making this for kids, it'd be a great way to approach (or re-enforce) the subject of plastics causing such damage. Make them in different colours, and styles too, and they might even catch on as a fashion accessory!
Great hunting & I'll be keeping an eye out for these myself (for my daughter) :)