They offer a silica product called Protekt that I'd recommend but it's not 'needed'. They also offer another product called magpro if you're using RO water. The only bottles you 'need' are grow and bloom and they'll last you a looooong time.
I've got nothing but praise for ProTekt as well.
To the OP, you asked me what I use to feed my girls. I haven't tried a lot of other nutes, but after trying a few other things, for my current grow I've gone back to Dyna-Gro (grow and bloom, I'll pick up some "foliage pro" when I run out of "grow" as I hear good things about it).
I don't use many additives, here's a short list of what else is going into my soil with my current grow:
ProText (silica/potassium additive, essential in my high summer temperature climate)
Compost Tea & 1/4 dose of
Great White Mycorrhizae (beneficial micro-organisms, added with food)
Plenty of
pH up/down (for a good pH buffer)
Diatomaceous Earth (mixed into soil, helps against bugs, and also adds a bit of cal/mag/silica)
Neem Oil (Also Dyna-Gro brand, occasional, very light doses, added to soil, helps against bugs)