Definitely use the DIY, I bought a divider and it failed the first night I had it...nearly lost one of the fish. DIY is easy, looks a lot better, and quite frankly, is cheaper.
I use a Whisper 10 filter in mine, the side across from it gets a bit of a protein buildup, but I have a voracious bubblenester (probably comes from having a female in the other half...) so he keeps it stirred up pretty well. When he doesn't I just disturb the surface by hand.
I'm no expert on water changes, and have a completely different bioload, so I'm not the one to ask on that :) Just putting in my two cents from my divided 10.