canuck4 is correct from what i've been hearing. not only do they use a pure powder, you get a more pure liquid. home brews will have glue, binders, and everything else that is crushed up in the mix including dust, bacteria, or whatever else can fall into a home brew mix.
it would seem you receive a higher mg/ml, clean mix, and naturally, you're paying for the service. i for one don't want to take the time to buy the fina, then the kits, then to make the fina injectable.
but to each their own. that's just my thoughts on the subject. i'm going to give some of these spectro products a try this winter. i keep hearing a lot of good stuff.