I concur that 50% WC, especially with ferts, is nothing drastic so as long as we're talking about fish here. That being said, WC are not necessary unless you're ferting regularly.
I can't speak to purigen but I do know that may people opted for a cheaper solution in Polyfill - the non-chemically treated pillow stuffing...stuff. I've had it in my Eheim 2215 for two years now.
Not only does it saturate first, its easy to throw out and refill and very cheap.
Polyfill keeps my tank crystal clear. I'm also not big on chemical filtration for a planted tank.