I've been thinking of getting / making one of these air filters for some time - my shed is full of dust. I read the details on the SIP, and have just ordered 2 of them. That will. I hope, make a big improvement. I will have to have a good clean up when I install them so as to start with a 'clean slate'.
I'll post my findings on whether they do the job when I have given them a fair trial.
For £25 each I'm not sure it would be worth trying to make one, by the time the filter is paid for, then sourcing a suitable motor/fan etc. To me the point is it's the sort of item you know you should have, but getting round to making one is quite another thing, whereas paying out about £100 each is not so attractive either. I've seen them on other sites for even more - £318 on Parker tools and Amazon, £122 on TW Wholesale, £195 on DIY Tools.
I don't think I can go far wrong for £50 for two. I hope not anyway - hope it's not a con, although he seller does have good feedback.
K