I am trying to replace a faucet installed on a small bathroom vanity,
and the locknuts holding the faucet in place are very difficult to
reach.

For anyone who has worked underneath sinks and replaced faucets, it
is usually tight quarters and hard to reach. It is especially hard
to hold a basin wrench or other tool in just the right position in
order to apply torque.

I have seen ads for a device called the Basin Buddy which is a
patented, supposedly universal basin nut wrench which claims to make
the job much easier:

http://www.wal-rich.com/BasinBuddyPage.pdf

Does anybody here have an opinion about this product or any other
better method of removing and tightening these locknuts?

It's a thirty-dollar tool that's only worth two bucks. It's made of
_plastic_ for crying out loud. You'll also have to buy an 18" socket
extender, and that'll run you another fifteen dollars or so--but at
least it will be metal. :-)

Of course, only you know what your time is worth.

--
Steve Bell
New Life Home Improvement
Arlington, TX USA