Another vote for the Ultimate Dust Deputy. I got mine when I needed to do some surface grading on concrete using a large angle grinder and 7-inch diamond cup wheel. The dust shroud was connected to the large, 50mm hose. The Festool dust collector had enough capacity, but the bag would easily get clogged. Turning it off/on to let the bag collapse and clean didn't help. I'd have to take to top off and tap the bag. The cyclone didn't totally eliminate having to do that, but it was significantly less often. This kind of grinding produces a tremendous amount of dust and I didn't notice any negative effect from reduced airflow when using the cyclone. So whatever the rate was, it was still sufficient for the job. And, it remains sufficient for woodworking tools including all my festool sanders and saw.
For general cleanup jobs, I used to hesitate using the Festool because of the cost of the bags and would revert back to an old shopvac. I hated the noise and the dust when emptying it and cleaning the filter. Now, I use the festool and DD. As an added bonus, the DD allows you to easily retrieve something you may have accidentally vacuumed up when using the Festool dust collector.
For on-site use, the Systainer like dust collector is big enough (IMHO), super strong and it is static dissipative. If you go the DIY route, be sure to test the container you are going to use to see if it will hold up to atmospheric pressure trying to crush it. Seal it up and use the vacuum to suck all the air out. You may find it will collapse in on itself.