I got my Craigslist tank! 5 gallons, already divided. Unfortunately, there's not enough holes to allow for both sides to be heated and filtered evenly. The filtering part I'm not too worried on -- the heating a little bit more. But it's been really warm here lately and I haven't needed the heater for my 10 gallon for about a week now. I suppose if I grab another thermometer for the other side and keep an eye on the temperature it should be okay. Now for the fun part...BETTA SHOPPING!! :D
Yeah, I found that to be the biggest problem with divided tanks is heating without having to resort to two bulky heaters. For filtering, just hook sponge filters up to a gang valve and stick one in each section. Works great.