I have had a FlashTrax for ages and use it at every motor race meeting I attend. Before buying it I had read that the battery didn't last too long so I bought a spare. There is no worry about keeping the spare fully charged for months if you don't use it. Just as well, I have yet to use my spare battery. I have a DC-AC inverter in the car anyway, so I can charge batteries for anything I have with me.
My positives for the FlashTrax are - Easy to use, quicker for download from CF cards than others I tested, very fast to download via USB-2 to the PC (or Mac for those that have them), updates readily available from their site and it withstands all the knocks and abuse it gets from working photographers.
My negatives - Display a bit hard to read in bright sunlight, that's it.
As far as looking at RAW images on it, or any images for that matter, why bother sorting images 'on the fly' when you have so much storage to play with? The only reason would be to use it as a display device for clients or family, and to be honest, even the FlashTrax screen is still too small to fit that purpose.
The only device I see working sports photographers using is the FlashTrax and we all can't be wrong. Oh, not one of us use it for MP3's, so either we hate music or have something better to do with our time. 