We've used a total of about 7 tons of gypsum in two different ponds. We used mainly the powdered (ag) gypsum, but we used the pellet version as well.

Here's my take:
That price is great, so I would definitely buy it and try it.
Gypsum definitely helped clear our ponds. I think the powder worked a little quicker because it can dissolve and bond to the clay better, but I think the pellet is just as effective in the long run. If nothing else, after the water is stirred up (rain or high winds), the pelleted gypsum that made it to the bottom should start mixing and working again. Think of it as the gift that keeps on giving.

There are many different ways to spread the gypsum. Slowly pouring it into the prop wash (from a trolling motor) worked well for us.

"Only after sorrow's hand has bowed your head will life become truly real to you; then you will acquire the noble spirituality which intensifies the reality of life. I go to an all-powerful God. Beyond that I have no knowledge--no fear--only faith."