Which Nikon camera you used to own? Because technically, I highly doubt that you're having "issues" with Metz 54 MZ-3. I don't believe TLA360 would be a better choice, because simply put, Contax N1's TTL flash control is far behind Nikon/Canon systems. That's why you're probably not too happy with results of your flash photography with Contax and Metz.
I own Metz 54 MZ-3 and bought primarily because I like controls (can't be any easier than that), quality, multiple TTL sync modules for different cameras, fast recharge times and extensive line of accessories. I have modules for Contax and Pentax, and thus can use the same flash on both systems. I used it on Contax N1, Aria and Pentax PZ-1P. With all three, I enjoy the results most if I make my shots with bounce adapter and 1/125 sec (and not 1/250sec!), because then I get a nice mix of ambient and flash light. Pop in NPS160 and you will probably like results even more.
Thinking about selling Metz 54 MZ-3 and getting TLA360? Rent it first, shoot entire roll, develop it and compare to what you get with Metz. Chances are, you won't see any difference and save money on switching it.
Also, there is a name and good engineering team behind Metz. And there is lots of hot marketing air behind TLA360.
Just my 2 all-american cents
Hope it helps and if it doesn't - discard the message into a pile of useless email.
Mike.