/usr/local, traditionally. Since it only exposes one executable anyways, I'd say the chance of clobbering is fairly small (and reversible, since it's a deb).
Augh! No no no no no no. Sorry, this is a pet peeve of mine.
/usr/local belongs to the sysadmin (I grit my teeth at FreeBSD's interpretation of this, much though I love the OS otherwise, and prefer NetBSD's addition of a /usr/pkg hierarchy to avoid jamming packages in /usr instead, which is only a bit less aggravating).
/opt exists basically for vendors to have somewhere to put things that they know won't trample on my /usr/local hierarchy.
(I still think they should've installed something in $PATH, mind, but /opt is not at all the wrong answer to my mind.)
