Charles, Love your post, Very well written and explained, Mucky, you as well. I think they are OK for mechanical filtration, biological yes they are designed to be, problem is, they clog, they aren't effective for much more than a fish or two and that's if maintained properly which few rarely are. I'm using a Zac Penn complete set-up. I love it but a complete set-up is not cheap. For a small pond a sower filter is a good start, Charles mentions the tetra trickle. that's the first time I have heard of it but I'm glad to see tetra stepping up to the plate for a decent over the counter filtration system, IF it works properly....
Why are you scared of DIY, it's a fun project, it get's you more involved with what you have going on and you can make adjustments to fit your budget and available space. There are so many to look into, Sand Gravel filters, Moving bed filters, up-flow filters, bog filters, and shower/trickle filters all can be easily be adapted, each has it's own drawback and benefits but they also all have been proven to work.
