I have to add that I only saw any flickering in the string of CFL's at the lowest levels - not in the longer, single tubes.
I remember TCP's guy saying that he "cut off the light" at the lower level so that it didn't lead to flicker.
If PSPM's bulbs flicker - at any ... the lowest, levels -- then, one can dim it down to just before flickering, or cut off the power earlier, before flickering similar to TCP. I don't recall seeing it's bulb flicker (one bulb), but maybe I could've tested it otherwise, and I don't know the power factor, cost or reliability of it for sure, nor if it dims AS LOW AS PSPM *WITHOUT FLICKERING*...and besides PSPM's bulb will probably be cheaper and last the 10,000+ hours -- don't know about TCP.
The longer tube -- i.e. the one that lots and lots of commercial buildings have -- did not flicker at any level that I recall seeing, and it dimmed just fine -- to just how low, what % i'm not for sure, but very reasonable dimming for a bargain price, plus daylight harvesting technology with sophisticated technology for auto or manual adjustments for (recorded) energy savings.
