Well, neck coolers may be less messy, but they can also be less effective. Sure, you avoid the brain freeze and the cleanup, but you're still at the mercy of that hot summer sun. A slushy, on the other hand, can provide longer-lasting coolness, even if it does require a little more effort to manage.
And let's not forget, part of the fun of cycling is embracing the ridiculous. I mean, we're the ones wearing spandex and helmets, after all. A little slushy in the pocket is nothing compared to that!
But hey, if you're worried about sustainability, you could always make your own homemade ice packs with reusable gel inserts. Just another option to consider.
At the end of the day, the most important thing is to stay hydrated and safe in the heat. So whether you prefer a slushy, a neck cooler, or a good old-fashioned water bottle, make sure you're taking care of yourself on those hot summer rides.