Well, after reloading for 40+ years on a single stage, and the last 20+ on a 550B, I can say that the progressive does speed things up. The problem, however, is in the extra steps needed to prep military-style (crimped primer cases), plus the length (trim) issue. In something like a Dillon 1050 with the Dillon trimmer, I imagine you could truly get progressive, as the 1050 swages the primer pocket during the loading cycle, plus you could trim during the loading cycle (someone correct me if I'm wrong),
That said, and being the cheapskate that I am, I process the brass in batches first before ever attempting to load it. It's sized on my Rockchucker, then trimmed & primer pockets swaged or reamed. Back into the tumbler to remove lube & the cases are ready to load. Like others here, I use a Universal decap die in my first station to ensure the flash hole is clear.
One thing to remember, however, is that if you can keep up with your fired brass, you never have to swage those primer pockest again, and I don't typically have to trim again for 3-4 loadings, so the loading process goes pretty fast.