I found a three part set of articles that I read a while back. They
give a detailed survey on hollowing tools in PDF format. It would be
good to look these over before you choose a new hollowing set. I have
included the URL link to each of the three parts:

http://www.morewoodturning.net/hollow-1.pdf
http://www.morewoodturning.net/hollow-2.pdf
http://www.morewoodturning.net/hollow-3.pdf

I found these articles are very thorough and extremely helpful.

Ted