Just wanted to point out a rookie mistake that I recently made in buying my first hydration belt in order to highlight one of the factors you discussed in your article.
Fluid capacity is REALLY important (duh)!
I bought my first hydration option (
NathanTrailMix Plus Hydration Belt) because I was
entirely focused on form-factor. I wanted a belt and not a vest because I usually run shirtless in the summer and who wants a vest tan...? Unfortunately that belt only has a capacity of 20 ounces and, with the heat being what it is now, this begins to become a problem on most runs over 10 miles. I can usually ration those 20 ounces on runs up to 15 miles but I really dislike stopping while working out (to tie a shoe, stretch, etc...) and pulling over for a pit stop to fill back up is like torture for me.
Apart from the capacity this belt has performed very well. It comfortably holds an iPhone X with wired headphones plugged in and some cliffblocks. The belt is comfortable and that is even true at race pace. I recently ran a half time trial in just a little over 1:30 and there was only minimal jiggle - nothing I would complain about.
As the temperature drops (and so too fluid-intake requirements) I think this belt will do the trick but if I could do it all again I would look for something in the neighborhood of at least 1L for a summer hydration option. The Ultrapire Speed Goat looks like a good choice because, as the article mentions, better to bring more than you need!