I had one of these in rotation at work for 5 years. 6-cups seemed to be the sweet spot on all levels. I would fill the reservoir and hold down the lever for a few seconds while turning the filter holder back and forth, let that breathe for 30s-1min and then plop the lid down and let it goto town.
To descale use a citric acid solution, I can't remember the ratio off-hand, but if someone can't find it online, I'm happy to find it in my notes somewhere. If you hold the brewer horizontal with the Bunn symbol down after taking off the spray head, you can drain the machine with little mess. Fill it with the citric acid and let it heat for a little while, longer depending on condition. Then either run water through or dump it like before. It definitely does get bad, my parent's brewer was so bad, CHUNKS of scale came off when I did it. Obviously this depends on your water.
I've had the thermal fuse go bad twice, the first time I replaced it for ~$10 and the second time I just switched to a new(used) brewer. Towards the end of its life, it was not keeping up with temperature. Frankly I don't know that it ever did because I only started measuring during the later days.
Easy way to tell if the thermal fuse is bad: If it is plugged in and the switch on the front doesn't light up when it is flipped to on, you likely have to replace that fuse, but fortunately it is easy to do.