This thing is a badly designed piece of crap. The way it works is it sucks in air through a tiny "pre-filter" (at the bottom), pumps it through the fans, then out through the big HEPA filter. The result is that the pre-filter gets clogged with dust almost immediately, like within a few weeks. I wager that 99% of people running these machines have pre-filters full of crap. Once the pre-filter is full of dust, the machine gets much louder and pulls much less air. Not only that but it starts pulling dust into the fans, which then get noisey and are hard to clean.
So, you are forced to constantly change the pre-filter. And they don't actually make a pre-filter that's cut to the size you need, they just sell sheets of charcoal paper, so you have to cut it yourself and it's a big pain in the ass (even if they did, they would be like $20 a pop which is too much since you have to change them at least once a month). I'm not surprised that they rate the HEPA filter part (on the outbound air) of it as "lifetime" because of course it's the prefilter that actually does all the work.
A properly designed machine should have a large surface area paper filter at the air intake.
The other problem with this thing is that it doesn't have a low enough speed setting. Even on lowest setting it is very far from "silent". You hear a constant loud whooshing. It needs a setting that's about 50% the speed of the lowest.
While I'm at it, let's talk some more about dust and filters.
I noticed that my HTPC has been getting steadily louder recently. The problem of course is dust. Dust makes fans noisey, particularly the greasy crud stuck on the blades which really disturbs the air flow. It also reduces their efficiency, and dust inside the PC greatly impedes airflow and passive cooling, so it's important to clean it out regularly (once a year is probably enough).
It would be preferable really to have little paper filters on the PC air intakes that you could just replace, but PC fans are not designed for that so it's not a good idea to add. The biggest PITA is probably the power supply, because the fans are inside the PSU block, and so are some nasty capacitors.
Laptops are a much worse problem, they have tiny passages that can easily get clogged with dust and ruin their cooling. Unfortunatley you can't really clean them without taking them apart. This should be done about once a year, or your laptop will be running louder and hotter than it needs to. I'm sure the insides of game consoles are totally clogged up too.
Some other random places that I clean that you might not be aware of :
The radiator and fan in the back of the fridge.
The fume hood above your stove. The grating for the hood gets filthy and clogged which ruins the suction. Soak in degreaser or just replace. The fan blades of the fume hood need cleaning too, though it's often hard to access.
Heater air vents. Obviously you replace the filter once a month, but you also need to take off all the output grills and clean inside them. I would really like to clean out the entire pipe from the air intake to the output points but I can't imagine how to do that. Basically forced air heaters are blowing giant clouds of filth and alergens into your air all the time and there's nothing you can do about it. One option is to put filters at the output grills, but most heat systems aren't designed for that much back pressure.
Inside your vacuum cleaner. Not only do you replace the paper bag, you take the bottom of the machine and clean out all the dust stuck in the piping. Your suction will be greatly improved.
The exhaust tube for your clothes dryer. Again you can't get to most of the tube, but most of the shit will be at the end near the dryer or the end going out of the house.