They last longer than a few packs of regular roundwound strings
actually, flats last forever, at least for the majority of flatwound fans
the first weeks are the breaking in period, and then they are settled to their sound, and still sound the same everytime you pick up the bass.
with rounds, even not using them wear them, because dust and humidity are string killers. when you leave a bass in the case with rounds, after a months strings will probably be "used" even if they weren't touched by anyone, in fact coated strings are usually preferred for "not used" instruments.
for example, I hate four guitars (two acoustics and two electrics) that I don't play every day; when I used to string them with normal strings, the plain strings rusted in a few days, nickel wound lost the brightness and bronze wound became green.
I switched to Elixir, and I can leave them in the cases without any problem, and take them out at any moment and feel "fresh" strings. (anti-rust on plain strings and coating on wound strings).
on the bass I've always preferred flats for the same reason, becasue once they settle, they stay the same forever. rounds change every day until they die...
