The pros and cons of using the time release soil verses the additives is an apples/oranges kind of thing.

You'll find the additives issues far more fixable than using that crummy soil. A lot of folks even like the MG additives but then you get into the heavy metals verses quality organic arguments and the discussion usually drops off into the deep end about then. It's a call you're going to have to make according to your own priorities.

Just stay the hell away from that god dang MG six month soil unless you want a good rump ramming.