The CTX is superior but if you buy new you may be left with buyer's remorse. The cost to value upgrading isn't that great, unless you plan on water hunting. I'd buy used, takes some of the edge off the price differential after selling the E-Trac. Sell the used E-Trac for $890 and buy the CTX used for $1890, you're only out $1K.
Thought experiment: If the CTX finds 20% more than the E-Trac (for every 10 E-Trac recoveries you get 12 CTX), then under the above scenario you'd only need to recover 60 gold rings worth $100 each with the CTX to make it earn its keep (equal the value added over the E-Trac). That is, the CTX finds 60 rings but the E-Trac would have found 50. That's a difference of 10 rings x $100 each = $1000 profit; you've made your money back.
So, buy a used CTX and go find the 60 $100 rings (or 120 $50 rings).
Or buy it brand new, now you only need to find 96 gold rings worth $100 each with your CTX (the E-Trac would have found 80) to make your CTX cost effective. Or just get 192 gold rings worth $50 each, either way.
In other words, unless you are on average very successful at this hobby ... just get the CTX, take the loss, and go out and have fun! Don't think about the money.
Johnnyanglo