I'm just accustomed to it and can dilute it for given jobs by eye. One of those "hey, I just like it.." product choices I guess. Before that I used P21s TAW for such stuff, but that one is *really* pricey.
I have 2, both are from a local detailing store here in NC, Majestic Solutions. I like the Super Green - 2:1 for tires, wheels and fenderwheels, and Tidal Wave - 1:1 can clean an engine and 10:1 will clean the interior. Never tried Megs so I can't comment.
i also like ms super green, on exterior since it foams a bit. and i use formulon 1 for interior and microfiber cleaning.
id like to try megs apc and apc+ but by the time it ships to hawaii its usually only a few dollars less than i can get some of the boutique products. same with optimum power clean.
Bunky & hplaceap- I got a bottle of PowerClean a while back, plan on using it when I start on the new beater-projects. David Fermani was simply nuts about the stuff.