I have not had it long but, I realy like my 406. It works very well, it's good and quiet I think the differances are as follows, with 406 Im pretty sure you get a extra media tray, the motor is suppose to be upgraded for better flow and for the big addon a better primer. I'll tell you what Fluval sure does believe in using plenty of sponges and you can buy whats called polishing pads in addition. For the money get the bigger filter you wont be sorry it always will give you better options when you upgrade. I've also noticed the africans seem to like the extra flow mine like to play in the outflow.
I too hate the white ends on the input and output on the 06's series been eyeballing other canisters with same dia. tubing to replace the fluval tubes. (My Marineland in/out tubes are all black its great, but wrong size tubing

). It seems to me after allot of reading most people can find a fault with just about any filter out there. My big thing when I started was getting that perfect filter which I don't think you will find all I can say is I am slowly upgrading and its on my list to get a second 406.