The dust bag attaches to a plastic fixture capable of accepting either 1.25 or 2.5 inch shop vac hose.
I was wrong. The dust bag attaches to a plastic fixture that looks like it should hook right up to a 1.25 or 2.5 inch shop vac hose. The plastic dealie is compatible with a 1.25" male shop vac but it does not look like it is possible to hook it up to a 2.5" system without some finagling. Guess which size shop vac system I use?
Thankfully I have one of those universal adapter dealies, so I was able to plug my shop vac into the vacuum port.
The only other ROS I've used is the 6" Ridgid (the model put out before the one currently sold, I believe it was made by Metabo). Compared to that unit, this one feels very small - not just the size of the disk, but the whole unit - I'm kind of glad that my universal adapter is prone to popping off, as holding it in place is about the only way to have two hands on the unit.
The power switch is on the front of the unit, and not where any part of my hand would naturally be holding the thing for sanding. My Ridgid uses a squeeze lever trigger on the handle. I wish the switch was located closer to where my hand would be.
On the other hand, this Milwaukee 5" unit is much less tippy than the Ridgid.
For large panels, I will likely use the 6" to 220 grit and then hit the piece with the 5" for 320 grit before sanding to 400 grit by hand.
Milwaukee has made a very stable unit to use, though the power switch isn't located in a very natural place. The incompatibility with 2.5" vacuum hose is a bit irritating, but the unit is compatible with 1.25" hose out of the box. An added feature is that pads for hook and loop or PSA backed paper are included with the sander.