That's the whole point of this thread. They are not going to be the primary filtration system for a 300 gallon tank granted, however they are useful for extra chemical or biological filtration even in larger tanks. Load a couple up with carbon, purigen, Phosban what ever and thrown into the sump is a handy way to use them for special applications. I use them packed with Peat & almond leaves in black water tanks among other things. I agree they are more suitable for smaller tanks up to around 90 gallons but can still be as useful today as they were 50 years ago. New hobbyists get caught up in all the new technology and may have never considered them for their ease of use, low cost and limitless versatility. This thread is meant to show they still have relevance even today if your willing to step back and be a little creative.