I started with Chemi-Pure, started using Purigen about 3 months in and I couldn't imagine being without, major water clarity difference. You have to bleach it to regenerate it. I don't bother with that, I just get the 3 pack on sale at Dr. Foster & Smith and swap out at the same time as the Chemi-Pure. I figure I'll try that regeneration thing on all 3 at the same time.
Right now I have:
Chamber 1 - Chemi-Pure on bottom, Filter Floss on top of that, Phosban on top of that.
Chamber 2 - Purigen
Chamber 3 - MaxiJet 1200
I'm thinking of switching the Purigen and Chemi-pure next time I add new product. Purigen works best with a decent flow going through it (like phosban).
I wouldn't start off using Purigen but as soon as you start getting fish and corals I would add it.