There appears to be a bit of a dead spot for smoke extraction on the entire left hand side of my unit. Smoke tends to linger in the air and it's really noticeable in terms of laser power drop off and smoke staining on the work piece. As I was buying some parts from Proto-Pic anyway I happened to notice they had a squirrel cage blower, at the low price of £3.30 it was worth getting one to try. It's a great, tiny unit, that moves a lot of air around.
I placed it loosely in the corner of my machine and bodged a power supply into it and you can see the improvement for yourself. The left hand wheel was cut before the blower, the right hand afterwards. Yes it's another moving part but it's significantly quieter than the other fans and pumps so you barely notice it running. I'm now acquiring another one for the other corner of the laser to blow across the whole work piece and then I'll get them both wired in and turning on/off with the main extraction fan.