I got a Penguin 350. It is a nice filter, but I had to replace it as my display tank had a top support that blocked a filter that large from fitting on my tank. So, I got two Penguin 200s. In the end I like that a little better. It gives me TWO intake points instead of just one with the 350. I have one that draws from the top of the tank and one that draws from the bottom.
The Penguin 200s, 350 and the Emperor 400 all have two slots (the 350 and 400 actually have FOUR, two on each side. You only need to use one floss cartridge in each side, if you ask me. I use a bag of ceramic media behind each cartridge. The ceramics plus the biowheel will never have to be replaced. The thing I like about the ceramics though is that I can give these to any new filter any time I want and have an instantly cycled filter for a portion of my stock with no concern about ammonia spikes, etc. As stated about every month I swish the filter media in a bucket of tank water to keep water flowing through it, but I haven't replaced any of these cartridges at all and it has been running like this since April. I did remove the donated media I added to my filter a while ago. These filters are great as HOBs go because of the extra space for other filter media materials. For my money the ceramics are the single best for biological filtration because they NEVER need to be replaced EVER! And they are easily transferred to another filter whenever needed.
Be careful about putting found objects into your tank. The answer is generally yes, but you want to test it first. Pour some vinegar on it. If it fizzes, you don't want to use it. If it doesn't, give it a good scrub and you should be fine. (I assume that these have never had any type of pesticide or herbicide used anywhere near them, correct?)