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So I just got a Rostock Max v2 and right away upgraded the hotend to one of the Hexagon models, as most of my prints are in PETG and need to be at 260*. It's giving me a weird issue though, I'll tell it to heat up to 255* and it will reach that temp just fine, but it won't hold it accurately, it constantly fluctuates 3-5 degrees regardless of whether or not it's printing, which is quite a lot. This is without any of the exterior cooling fans running. I've tried PID tuning several times with the code M303 S255 and it starts just fine and runs through a few cycles, but then it just stops without giving me any finishing values. I'm at a loss here, any help?

It should be outputting lines of information to the gcode console in your host software the entire time it's doing the autotune. Is it not?

What do you mean by finishing values? The printer gives you 3 sets to average together yourself, rather than doing it for you. If those don't suit, I would work on manually tuning your PID. Likely decreasing your I value is what you need. Manual tuning, while sometimes tedious, will be better than an autotune in almost any case. See here: https://www.instrumart.com/pages/202/ma ... controller

That being said, what is your reasoning behind the Hexagon hotend, rather than a better known one like the E3D V6 or Prometheus?

It is outputting lines the entire time, yes. I got it to complete a full tune finally by starting at 205 and inputting those values, then 225, 245 and finally 255. I still have the same problem though.
The Hexagon was ~$50 and the reviews on it were in line with those of the E3D, and being that the Hexagon is so much cheaper I naturally purchased it.