I doubt either is deeper than the other. CZ's will handle bad ground better but since your soil isn't bad, this may not be a factor to you.
The CZ6a is an older unit so I don't know how part availability is. May want to check w/Fisher directly on that.
Tejon will be much lighter until you hip/chest mount the CZ then the CZ will have a weight advantage (for swinging).
8 AA's vs 2 9v's
CZ6a is water resistant if that means anything. It does not have an external speaker so headphone all the time will be necessary.
CZ's are deep coin hogs and don't need a lot of sens/gain to do it. I love mine CZ (CZ-3D) but they can be weighty. I run mine hip mounted as often as possible unless I'm in heavy grass, brush etc because the coil cable can hang up.
Couple more things about the CZ's…SO easy to use and learn and they run very well with low disc and low sens and don't get "chatty". You can run em over the presets and and still have stability in high emi areas. I targeted a deeper coin ('54 wheat) yesterday and I kept turning the sens down till I couldn't detected it any longer. It was almost at the lowest setting before it disappeared. BTW I NEVER run my sens over 5 with 10 being max.
Depending on how cheap you can get the CZ for, that's the route I'd go. Won't be out much if you don't like it. People that own em, rarely let em go. Reason for that.
I have no doubt the Tejon is a great detector too.
Good luck on whatever your decision.