I have two Z3's....a 3-10x42 and a 4-12x50 with the BT. I like the BT better than the CDS, as you can set up the BT anyway you want on your own without having the mfg engrave or supply anything further. For basic hunting use, I think it's pretty good. It's very similar to my single-pin sight on my hunting bow, at least in concept, so that might be why I like it so much.
I don't like the concept of the custom-engraved CDS. Change your load, your dial is cooked and you need to pay for another one. If you're into MOA-based turret spinning, the MOA CDS probably makes more sense than the BT, but for most hunters, I think even the BT goes unused, as most of us simply don't have a need for it. I have it because it happened to be on the scope when it appeared for a good price.
I have my Z3's because they were priced right. I got the 4-12 for 750 and the 3-10 for 650. I have thought of having them retrofitted with #4's. For what I have in them, I'm still not at a bad price, and probably makes them more capable in low light. The optics are, but the duplex reticle isn't the best.
