I will admit that this past season I purchased the liquid CYA for a few reasons. I am impatient and needed it. I also wanted to know more about it as an option- a thick liquid that is best used if you're going to use the entire bottle at one time I think because it might be difficult to measure (for my pool the entire bottle was enough to bring my CYA level up aprox 35ppm).
When I use granular CYA I hang it on a pool noodle and let it float around. It takes a few days to dissolve, and I don't want to leave it in the skimmer because then I'd have to run the pump 24/7 (CYA has a low pH and if that CYA rich, low pH water sat in the skimmer concentrating...well, that's a big bolus of low pH water to hit the pump and equipment all at once when you do turn the pump on. Kinda harsh, huh?) So in this case I tried the liquid. I liked that by the very next day I could test for CYA reliably unlike granular CYA which takes up to a week to show up on the tests.
So while I doubt I'll use it again, I might if ever I get impatient again.