Been through a whole lot of 12AU7's recently on a "quest" of sorts. I finally settled on the RCA triple mica black plate 5814's. They seem to do it all.
The Mullards definitely have an appeal, and do sound different from most other tubes. However there's too much to give up with these to get that seductive midrange. The top and bottom extension just isn't there. They are not neutral sounding. However, as I said, what they do have is very seductive.
Bob