I had a VO sprung saddle and the nut would constantly loosen up, like several times a day. This has never been a problem with any Brooks that I have owned. I also didn't like the fact it required two tools to adjust tension. VO was great about it and allowed me to return the saddle in exchange for a new Brooks. I also have an unsprung Cardiff saddle and it is similar to the VO so I am guessing the same manufacturer. The Cardiff is beautiful but squeaks like nobody's business. From now on, only Brooks for me thanks.
Having said that, I love VO and they make great stuff whether you are into retro or more current bikes.