I used them for a bit, I found them to be all middle, no real low end (no depth of low end anyway, mostly low mids), and they didn't have a great top end either.
I also found the tension to be too much, I use a medium gauge, but I like a string to be quite flexible.
I've gone back to using DRs, they sound so much fuller across all the frequencies, and are really flexible, they just respond to the nuances of your playing more, they let you play .
At the end of the day you either like something or you don't, and with Elixirs there seems to be a pretty even split between people who like them, and those who don't, there are dozens of threads on talkbass about them.