It's not necessarily better, just different.
Not as transparent as the U5, and has more EQ possibilities. The EQ in general is great except that the top end was clearly designed with sparkly vocals in mind, not bass guitar. It's set to give a lot of presence on top, and I find it largely "misses" the top end of a bass guitar,
The compressor is the weak link in the chain. It's has a very slow attack. People have been known to mod these to increase the attack time.
If I were in the market for a 2U mic pre for studio use, I'd look at the UA LA610. Definitely not the same vibe as the Avalon, but a lot more useful in a variety of settings to my ears. Works great on just about anything as long as the input isn't slammed too hard as it will clip a bitter easily than some other mic pres.