How often do you change them?
Depends on how much I gig/practice on a bass after it's strung with new strings, but I can get adequate life from them for about 15 days of heavy gigging and band practice, but I play metal and a lot of slapping. I am REALLY not precious with my string, they get a lot of abuse, which reduces their lifespan drastically.
It was the same case with d'addarios so they aren't worse than d'addario nickels, and I'd say that's what they mostly sound like. They do feel smoother than d'addario nickels, though, I don't know what causes rounds to even feel smooth, but there's that too.
I mean, if you're ordering something from thomann, it's easy to chip in another 5e to get a set of strings to try them out or have as a backup, but now I order specifically strings from thomann if I am playing a lot, because they're good yet low cost. I've strung both my spector and jazz bass with them and they are adequately bright.
Something to note: I've heard people complaining that 5 sets come with dead B strings, which I can't confirm, but is something to look into if you're playing a five stringer. As for 4 string sets, sounds great, and I've tried them many times without fail!
Don't know how much it costs to ship thomann products to the US, but it's very cheap in Europe, so it's great stuff!
It might sound like I'm cheap, but really, an actual average (monthly) salary in serbia is about 200 euros, so buying 20 euros worth of strings (which d'addario nickels would be) is insanely expensive since it's about 10% of an average paycheck.