Couple of days ago a fellow tech asked me how do the two scopes differ from one another. I have the 3423 ....I think...it has worked great for many years....performs great....how much better  would the new be? Would it justify the investment?

Feel free to share your opinion...Thanks

The tutorial movie library has a couple good videos on the 4423 and 4425 performance.  The 3423 is mentioned many times in the 4423 video.  Over time, Pico made improvements to their software that helped the performance of the 3423, which is stated in the video.  There's a 3423 sample rate chart in a forum post from 2008.  

It would be a very large jump in performance from a 3423 to a 4425 or 4425A.  Sample rate, ground offset, need for attenuation at 50V vs 200V are some major differences 3423 vs 4425/4425A.  Sample rate will effect how the scope can be used, this alone would be enough to justify the expense of a 4425/4425A.  The 4425A performance is the same as 4425 but the 4425A adds features such as powered probes to allow graphing of resistance, automatic probe type detection, auto-zeroing current probes, no batteries in current probes designed for the 4425A.  If the PC has a USB 3.0 port, the 4425 and 4425A can take advantage of that for fast file transfer. The 4425A is expected to utilize this 3.0 port for future probe development.  The probe improvements is reason enough to consider a kit rather than a 4425/4425A scope only.

Thanks for taking the time; specially to emphasize the strengths on areas that Pico users will notice right away. I got my Scope 12 or 13 years ago.....maybe longer and it's reliable and faster than most scopes out there even now. Honestly, after I got mine I stopped looking for the next scope.
I thought the newer versions were changed cosmetically and at a lesser degree on performance or functionality but obviously I was wrong.

Thanks again.

For me big advantage for 4425a is differential channels and power supply over BNC, no longer need to wear spare 9v batteries