I wouldn't personally drink Hoist or any water that added sugar. We eat enough sugar in our lives, save it for dessert. The reason for all the waters is economic -- people cut way down on drinking soda so people started selling flavored tap water. Some added vitamins and minerals. Some are copies of Gatorade, for electrolyte replacement, but they add sugar because it's supposed to hydrate a hard-working athlete faster. Obviously, nature created us to drink pure water and nothing else. It must have worked, because humans are still around. The rest are either supplements or just another sweet. We like us some sweets, and we like variety of taste. One problem with this is that putting nutrients in a bottle of water, which is usually clear, leaves it open to oxidation as it's shipped and stored. This degrades the nutrient added to it. You also lose a lot if you don't drink the whole thing quickly once it's opened because again it will oxidize and degrade the nutrients. They aren't protected from light and heat as vitamins and supplements are in dark bottles and enclosed in capsules or tablets. But mostly they are just popular because we like the taste. Serious athletes, of course, use sugar quickly and it gives them a short term boost in energy. Most athletes only perform for a short period of time so there's no crash. It's like the chocolate milk craze -- milk can decrease performance because we lack the enzyme to digest dairy, so it can cause inflammation and sinus congestion but it has sugar in it and tastes good. It's all about the taste, because taking a supplement or eating a whole food would always be a better way to take most things they are adding to the water. But as long as there's little or no sugar added, for the average person, no real harm in it, and again, for an athlete, they are much more concerned about performance than they are health and any psychological boost helps them.
If Hoist has electrolytes in it, and your son is sweating a lot, it is probably fine for hydration.
As a runner, especially now in the summer heat, I take electrolytes after every run. (I do in the winter too.) Before I started taking electrolytes, I would sometimes get calf cramps or have muscle twitching after runs, which thankfully has all stopped since I started electrolytes years ago.
I usually buy electrolyte powder packets because those are cheaper than bottles and are often low in sugar, and I usually mix it in to water after I get back from a run, but if I am doing a long run, I might drink it on the run. I have found my body is very sensitive to any electrolyte mixes that contain magnesium (not everyone's digestive tract handles certain forms of Magnesium in sports drinks), so I'm very careful what I order now (Generation UCAN electrolytes which contain Magnesium phosphate do not work for me).
I've been using Propel electrolyte packets which you can usually get about 5 boxes of 10 (50 servings) for around $10 on Amazon. (What can I say, I'm cheap and I often take 2 on very hot days). I've just ordered some Gatorade Thirst Quencher powder, which comes in a canister of 94 servings for around $10. That one has more than the 0 calories that Propel electrolytes have, but I like to try new things and I'm fine with some extra sugar after a run. There are a lot of different electrolyte powders out there and many would probably work just as well as the sports drinks/smart water bottles.