My experience has been good.
They approached me about 2 books which had done very well, and I essentially blew them off because the advance was not enough to justify tying the books up for 7 years, and they were not the books I really wanted made into audio.
Unexpectedly, they not only read what i said, and paid attention to it, they came back with an 8 book deal, which included the unfinished 3rd book in the series they wanted, and the first 5 books in my first series. And with a significant upping of the money to something I couldn't ignore.
I was also talking to Podium at the time, and Tantor just blew them away with the second offer.
I also got cover veto rights, so before each new book goes out, I get sent the cover they want to use. The first ones were easy since the cover artist simply did new ones. The rest were covers I made myself, and the first of these took a bit of getting right, with some work on my end to better the quality.
6 of 8 done now, with the other 2 due out by the end of the year. And this is well in advance of what the contract said regarding production deadlines.
So far, its been a positive experience working with them.