[chriswood1900]

One thought about anything that relies on digital software is that it will only work as long as the necessary software and operating system is available and supported otherwise you are into keeping old computers running just for your piece of test equipment. I already have that problem and can assure you David S's analogue world is much easier!!
This is not to decry some excellent test equipment just a fact of life. A computer based valve tester is less likely to still be capable of working in 40-50 years unlike an AVO.