I was in the exact same boat - I wanted a PTO driven chipper, something that could handle 3" or less.
I looked and realized that even if I spent a grand on one - the machine (B7100) would be too small to do the job.
What I did was find a gas power chipper - on craigslist, good ol DR Chipper - it pulls behind the tractor, 10hp briggs - works like a charm. I have used it often and it works well. Just my 2 cents.
I dont have any first-hand experience, but there appears to be no shortage of people using chippers on their BX to chip <4" diameter limbs. Search youtube, see for yourself.
Not sure about investment but its certinly a long term attachment. I have had mine several years and I think the hour meter reads 12.3 , lol. The Woodmax is self contained and the power feed that pulls the brush and limbs right in much easier then pushing all the brush in.