These are relatively new strings. We've bantered a little bit about Presto being Eurosonic, but I think presto is now distinctly a different string that euros ever were.
Herve' Jeanne's string sound samples page include Presto Hybrids, and I must say their arco sound is the best on his page:
http://www.hervejeanne.de/saitenmatrix.php
I'm 99% arco and have a bright 2003 Romanian carved bass. I'm after a dark gut-like arco sound (aren't we all). Currently I'm using the popular flex/spiro top/bottom combo.
Does anybody have any recent experience with Presto Balance strings? See also:
http://www.presto-strings.com/balance.html