Since I am biased towards the analog CZ's ( have 2 6a's that will never be sold as well as a CZ20), I say hold out for a bit to see if a CZ5 or CZ3D comes up for sale. Not sure if any 6a's will be up for sale. I think guys who have them realize they are the best of the bunch overall since they are more air/water resistant, can take a pounding and all of them are on par with each other depth wise so there wasn't much if any variance between one and another one. The two I have, one being one I bought when they first came out, and another I bought used about 10 years later, are identical in depth and how they work.
The main reason I like the analogs is they are a bit quicker to respond, I like the meter system, and you can fine tune the sensitivity. Can't do that with the digital CZ's. The one thing the digital units have over the analogs is the notch feature, but that is something I never use.
If a CZ70 Pro comes up, that would be the digital CZ to get in my opinion. These units are just as easy to use as the analog CZ's, and they have a 4th tone compared to the CZ5 or 6a. The CZ3D has the 4th tone too, as well as an enhanced mode. I had one but sold it since I was mainly beach hunting at the time and did not have use for the enhanced mode, but it was a great unit. Wish I kept it. It was one of the ones built at the Los Banos plant, so if one of those come up for sale, it would be a good buy. Not saying the newer First Texas CZ3D's are bad, but in reading reports/opinions, it seems some are not as deep as others....but I never used a newer one to confirm that. I believe that those who had the newer CZ3D's and had issues with depth, were sent back to First Texas and made right so that is a good thing.
Since they still make/service the CZ3D, it would seem that they can also service a CZ5 or 6a since the components are similar. Not sure about servicing the digital versions.
