[exim] exim and p0f - any suggestions?

I am about use p0f fingerprinting with my exim + amavisd-new + SA

I want to use in exim acl external shell or perl script to take distance
and OS from p0f, then put with warn X-p0f header in incoming email and
with amavisd-new and SA score spam based on that header

What do u think about that? Anyone tried this approach? What are
disadvantages and pros with that solution?