I've had two since the late 90s. It's a very intuitive system as you add what's needed. Need more red, add more red. I never used the probe. I found I was always where I needed to be within 2-3 test strips. The most annoying part of the 45A is the focussing. It has a separate flashing focus tube that is limited to 30 seconds or so. So every time you focus you feel the pressure to get your negative focused before the flashing stops. If you hit the focus too many times you can overheat the system. As Brian mentions Darryl Nicholas is the guy for this system. His company is Colorbat and its still in business although they no longer focus on the 45A.
http://colorbat.com/search.php