I mount two rear lights. A planet bike superturbo flash and cygolite Hotshot. I run the turboflash on steady using lithium batteries and I did have to replace them once on PBP. I never run the Hotshot with other riders near as it is run as a blinky. On bad roads and depending on what intensity one has it dialed up to, it gets motorists' attention. Of course, you have to aim any rear light correctly.
I know this is a controversial statement but the dynamo rear lights are not very bright and I have come up on hundreds of riders who use them, I would mount a blinky in addition to one of those for times on less than optimal roads like narrow ones at sunrise or sunset.