Hi Mock,
If you are having one extractor for both dust and courser chips then you will need one with a fine filter, 5 microns type I believe, to catch the harmful particles. A number of members use a cyclone on the line, hopefully someone will come on to explain that - I don't have one. If you have a separate extractor for the courser stuff from a planer then one of the 2 bag types will do the job for that, and use the finer filter machine for your saws, sanders etc .
Axminster have both types. I use a Numatic 750 single motor and one of their Hobby range double bag type, can't remember the model number. Another reason for me having 2 extractors is that my planer thicknesser is in the garage, everything else is in my shed.
Hope that's of help.
John