Hi Rich,
I have an axminster extractor in my dad's woodwork workshop, and hands down is the most useful power tool in that workshop. It is one of the dual-bag types (with a filter bag on top, and a collection bag underneath)
That being said, if I was to use it with metal shavings and swarf, I'd def' want a cyclone seperator unit before it, just to protect the impeller blades ( metal on mine ) from the heavier stuff.
You can easily build your own seperator, if I recall, Axminster used to sell a cyclone lid to fit a standard dustbin.
The other problem might be when you use cutting oils, it might not do the filter's/filter bag too much good.
Tim