We adapted the dual design for two Honeywell North filters, or one 22mm ventilator filter.  We have only performed quantitative testing with the 3M design yet but will update this log with the results once we've done the others.  All three designs are here.  We tested the 3M design printed in PLA and coated in XTC 3D coating.  We're also printing in e-Rigid PU resin on an EnvisionONE printer (EnvisionTEC).  This is a semi-flexible airtight material that should be able to be used without coating.  We will confirm and post back after quantitative testing, but prints look very nice!

Here is 3M P100 adapter:

And the threaded Honeywell.  Unfortunately the threading on this has not worked out for us - we will keep tweaking the design but we think it may be difficult to print the threading precise enough.  One side is working but the other is not threading onto the filter well.  This was printed on the Envision ONE which has pretty high resolution.  We also tried in PLA on an FDM printer with abysmal results :)