I personally wouldn't bother with EI for little tanks. Dosing with TPN+ is so effective & easier. At least for me. Now the 450 is a different matter & EI ( estimating index), a method of fertilization based on dosing the nutrients & then resetting the levels with a waterchange, is actually a very inexpensive way to provide nutrients for planted tanks. I did it once, and liked it, but my current setups don't really need it (small tanks or lighting is lower) Once you dose EI, though, you could produce enough ferts really do all the tanks fairly inexpensively. Some people have problems with it, but I think it's due to other factors, & not necessarily EI.
Liz