I actually bought some stainless tubing with the idea of having an "all-metal" option for ZT-HE, but the problem is cutting it square with nice, burr-free edges. Didn't really pursue it.
Even with an all-metal hot end, it's tough to get the required temperature with the Zortrax heater. You need to enclose the printer, have a well-heated room, keep the fans off, and wait a long time. I don't think I've gotten it above 320º.