They are cheap and good for timelapse, especially since you can control them so nicely via USB, they are good in low light and you have good bulb ramping options.
In after effects go to linear color space and float for your composition. Then just key brightness, as long as you shoot within histogram they keys will keep the brightness constant. You can do this in a log space but I find it real hard to key the brightness correctly. (when doing this in linear, output it in log when your done)
As long as it's a metadata only change, when you drop the r3d into AE with linear using float, the AE in memory floating point numbers for color/brightness have enough bits to hold all the data (is expensive on memory and speed). By keying the controls (i.e. multiply color values/brightness, etc), you can keep the screen brightness the same though the r3d is changing. It is hard visually working this way, since the data is in the float and when the float get's converted to 8/10 bit for the screen it will get clipped, but by keying multiplying values you can keep what you want to see in the range where it will not be clipped. In nuke it is a bit easier to do this, for nuke you would output in redcinex in exr 32 bit mode, making sure you don't clip any of the r3d footage in the histogram by just doing a rgb multiply(or just link in the r3d if your using a older r3d type then do the multiply, using the "none" color mode). Then in nuke automate/key the color correction (nuke also works default with a large floating point numbers in ram). This works as long as the original shot data is within the camera histogram.
