I have the 2 mode R4. The difference in brightness between the two modes is so minimal that determining which mode I'm actually in takes a few switches between the two, depending on conditions. I find this rather frustrating and if I had known that before I bought it I would have chosen the single mode unit, if it is true that it is slightly brighter than the 2 mode I have, even if it were a tad more expensive rather than slightly cheaper by a buck or so, IIRC. At least with that light you are getting slightly higher output (it is said), you always know what mode you are in 'cause there only is one, and in theory the run time is consistent and you don't have to use complex math to determine how much time is left based on what percentage of the time you were in each of the two modes (that is if you can even tell which mode you were in!)
Not a big deal and a good light overall though. The added run time potential, [does anyone know how long?] could be important to some, more so than my slight quibble.