I use the seachem stuff, but have still tried to get into the habit of doing 50% weekly water changes as I'm shortly to be switching over to EI. However, I don't believe that there is the same requirement to do large WC with seachem because you are not (unless you have amended your routine) overdosing the ferts if you are following the quidelines on the bottle.
The point of the big WC on EI is that you are dosing an excess of all nutrients to ensure that the plants have sufficient to grow, but you need to remove that excess weekly.
If you have a tank of any sufficient size, the Seachem route will end up expensive in the long run.