I first came across Elixir strings nearly four years ago when I bought my Ibanez BTB 6. They were pre-loaded on the bass. Even though the bass had been in the store for a while and had been played by numerous people, the strings sounded great (played in, as others have pointed out).
It was quite a while before I needed to replace them and even then it was mostly because the coating was starting to disintegrate over the pickups where I play finger style. The tone was still good. This was after a dozen or more gigs and an equal number of rehearsals. I currently have three six-string basses and a vintage Ovation Magnum I, all stringed with Elixir. To be honest, I don't like them so much on the Ovation (perhaps as it is passive and the others are all active? Im not sure) and may change to uncoated on that bass. As it doesn't get gigged too much, I suspect the strings will last OK.
Equally, one of my six strings is a Sei headless and although they feel and sound great on the bass, I don't like the Allen bolt locking mechanism at the nut for non-double-ball end strings (I even pulled the low B out of the allen bolts grip last week stretching the string whilst tuning) and as Elixir don't do double ball end strings, I've bought some Hotwire round wounds via the Status website (great price) for this bass when the Elixirs need changing.
JTE - they do two string lengths (for the B at least) so you may need the extra long set for your bass.
So, going forward, I will continue to use Elixirs on two six string basses.
Incidentally, the other six-string is a Cort Curbow which I have strung E to E a la baritone guitar. Using a standard Elixir set for the lower four strings, I bought their 'high C' string for the B string (are you following this?) but they don't produce a gauge low enough for a high E. I therefore had to use a single (uncoated) .22 from another manufacturer. Not ideal, but I'll see how it works out...
I mostly used Rotosound Swing bass on my basses for the previous 30 years, so it was a big thing for me to change. I agree with most other posters on this thread that the strings sound just about played in from new but they stay that way for a long time. How long they last will be down to your playing technique, aggression level and hand/sweat acidity.
Yes they are expensive to buy, but as they last so long, you need to work out what you would spend on your regular strings over the same period. For me, there is a value advantage.
Bob