I have a big 2hp Griz dust collector. It may have a 5 micron bag on it but after you run it a while layers of dust build up on the inside of the bag and it traps almost everything. I have virtually no dust transfer outside the collector so adding a bag to your drum will give you an almost dust free environment.
The picture is of the unit running, the bag collapses when it is turned off.
The dust you see in the picture on the motor is from me cleaning out the bamboo fibers from the blower suction that occasionally stops up my piping.
They make a 30 micron filter bag but it is pretty pricey.
One other thing, even with the dust collector I have a lot of dust in my shop because the bandsaw and belt sander aren't sealed well enough for the collector system to catch everything. I installed the dust collector in an adjacent room to keep the noise down in my shop, that room is dust free.