Henry, Festools, Mirka, Feins, Vax, Numatic and a whole host of other brands supply vacuum units that will suffice for power sanding. Think about 5 things when speccing a vacuum - filtration, suckability power, capacity, ergonomics, noise, accessories
Having done a fair bit of research, including seeking advice from a H&S expert who also sold and specced vacuums, there are 3 types of vacuum, related to their filtration capabilities.
The H-type Haz Mat safe units are 99.95% rated ie with suficient Hepa filters to contain 99.95% of all dust sucked into the cannister, that would be Festools post march 2012, and Numatic HZQ for example, two I am familiar with.
Then you have type G which to all intents and purposes are builder quality (and general decorating) which are good for 99.5% filtration.
Then standard vacuums with a simple bag and filter.
Having bought a Haz mat vacuum, unless you are wholly heritage sector restoration dealing with lead or asbestos, the 99.95% filtration spec isn’t worth the extra money.
Never use a vacuum without a bag, unless you want to shorten the life of the machine or prematurely clog up your (expensive) Hepa filters. The bag is counted as a filter.
Any industrial vac has enough power to deal with dust extraction. In fact, commercial grade like a Henry are sufficient for power sanding. Your Miele home vac is OK too, for power.
Like any machine the more robust the motor the longer it will last.
Although powerful enough, you need to consider filtration and capacity before relying on a household vac for a complete house redec.
Numatic do twin motor units. Festools are quiet and dependable for hour after hour, Numatics are dependable too. If you are doing exterior work and continually vacuuming rubble and brick dust, I would get a beefy £200 Numatic twin motor vacuum for that particular heavy lifting, it is worth it.
Henrys are powerful and lightweight, but they have a small capacity bag. With a CEROS and Abranet on extensive filled walls, it can fill in an hour. For odd DIY projects, or your entry into dustless sanding, it is a great vacuum, but constantly emptying does add to the cost if you are a pro. And if like me you are incapable of emptying bags before they get full, you will repeatedly stress the Henry if sanding a lot and often.
So when considering capacity, the industrial size vacs are my advice for serious users.
Check out Jack Pauhl for 100 ways to improve the usability of a vauum cleaner. Bottom line, the Festools and Mirka models have been designed with the decorator in mind. I am not sure any other brands have. Certainly not the Numatic I have.
I suppose if you wear ear plugs, it doesnt matter to the user, but some units are noisier than others. Hum is better than roar.
The vacuum extractor unit is just a box with a hole for a hose. To make it useful for decorating, you need hoses, head attachments (brushes, wide head, narrow head) ways to fit hoses to tools, extension cords, containers for tools… And you need ot be able to extend your extensions, etc
Festools and Mirka have thought about the accessories, Numatic have a huge range of upgrades that work across their range of vacuums, but you need to make sure your tools will attach to the hoses etc, and sometimes a roll of duct tape is essential.
I dont think there is a best value…
for decorators, for looking and being the part, spend out once on festools or mirka;
to do the job well but less integrated, £150-£200 industrial vacs offer the power and capacity,
£100 will get you up and running, may last several years, or may not.
This link will ring up a few articles on vacuum sanding units, including mods etc