I've been using Part A (5-12-26) on and off for about 2 years. I like to try different brands and mixes, but I keep coming back to MC Part A alongside a cheaper generic brand of calcium nitrate. I get consistently good results with it and often a magnificent burn. I'm not crazy about the smell of it and it needs to be mixed at least 15 minutes before it's used because there is small amount of it that requires a little extra time to dissolve. I've speculated to myself regarding what I believe to be the reaction involved but I don't know for sure, however I can testify that it completely dissolves with the added mix time.
It's so cheap compared to many other things that I have used and it never clumps or gets sludgy, even in a poorly sealed container. An absence of ammonium nitrate certainly helps with the shelf life. About a 2 year supply of it is comparable in money spent to about a 2 month supply of some of the "fancy label" liquids that I also love.