Here I am agreeing with the Professor again (but trust me, I'm not a groupie...).
An emissions-only tester is practically worthless for testing audio tubes. Read this, which is not a bible by any means, but sums things up decently::
http://www.tungsol.com/html/faqs7.html
A mutual conductance tester is far better, but even most of those that can be had for less than $1k (Hickok's, B&K's, AVO's) have limitations compared to a laboratory tester. Still worthwhile to check for shorts, leakage, gas, and can be used for matching to a degree. I have a Hickok 752A that has been a good tester for making sure Ebay-sourced tubes don't have flaws that could cause problems in my equipment, and it's been helpful for rudimentary matching (between tubes, or between triodes in twin triode tubes like the one used in the Lyr 3). But you can expect to pay at east $750 for one of the better Hickoks in decent condition, and substantially more for one that is refurbished and calibrated. Buying one that hasn't had either is a fools endeavor, as 50+ year-old caps and resistors are a ticking time bomb for failure, and a 50+ year old unit that hasn't been calibrated recently is going to be worthless as far as accurate readings.
All that said, they're fun to have and fun to play with, but unless you're going to be testing a LOT of tubes (or have green stuff desperately trying to escape your wallet), it's a lot of money for something that doesn't do a thing to improve the sound of your system. There are quality vendors out there that will test tubes for you for a reasonable fee, and typically have much better equipment to do a far more comprehensive test.