It uses a groovemount system that is nearly identical to a J-head (with the tiniest smidge more space for the screws as aluminium doesn't deform as much as PEEK in a JHead). You should be able to use any J-Head groovemount type extruder. What printer are you using?There are a few reasons we went for a short thermal break -1) First is that it confines the melt point/transition to a very specific place, which gives consistency in many aspects of extrusion. This is borne out in personal experience, but you are right - some sort of more quantitative and empirical measure of this is really needed for good comparision. The theory is certainly there, and stratasys detail this very very exhaustively and go to HUGE lengths to ensure a consistent and 'locked' melt point on their FDM machines.I am unsure of a good way to measure this - high framerate slow motion video of extrudate exiting the nozzle with a view to observing a sharp start and end to extrusion would be really nice.Perhaps I will retrofit an extruder with a long break and try to do some comparison prints using the same GCODE on challenging items such as many towers where stringing may occurr. Suggestions welcome.2) Extrusion force - As filament goes above its glass transition temperature it becomes rubbery, buckles somewhat, and begins to adhere to the walls of the tube it is being forced down. Once filament liquifies it no longer impedes the travel of filament behind it (setting aside backpressure etc). The longer your transition the longer your amount of rubbery filament, more rubbery filament - more adhesion, more adhesion means more force. This we have absolutely experienced this too - but if I get an extruder with a long break rigged up I will try and measure it.3) Manufacturability - You will notice how long it has taken Prusa to get to market, drilling these long holes in 300 series stainless steel is not easy, or cheap. Then talk about reaming/polishing the inside too. Prusa seems to think that a 1.75mm version of his design might not be possible, and I would agree with him, the hole is too deep and too thin.The reason we can sell these for the price that we are is because this whole setup was designed with a specific lathe and specific tools on that lathe which makes manufacture fast and easy, therefore cheap. It seems like other hotend designers have come up with thermally fantastic designs but have utterly disregarded the fact that someone actually has to make it!In all seriousness though, I genuinely think PEEK is a possibility - our efforts to get some made for us have so far been in vain. However we are looking into self-extrusion of granules to get around this. I would also love to print FEP,(A fluoropolymer like PTFE in many ways, but can be melt processed) would be amazing for bearings and such, but I imagine it won't stick to anything... ideas? Perfboard?Yeah, that is a stupid omission, we have update our site to include this prominently. We are moving to an entirely new and improved website/hosting soon so watch this space.It's tight between those rods with them being 50mm apart and the hotend being 30mm at its widest, but it does fit! (Just) Depends a bit on the XCarriage - Kuehling style ones fit beautifully. Gregs style ones are a bit small between the bearing holders, and you would need to nibble away about 1mm of plastic on the bearing holders to fit. Alternatively you can duct/mount the fan elsewhere or integrate a fan mount into an XCarriage.The link that Cameron posted should take you right there - the website isn't great, and we are trying to change it rapidly. If you are having any problems I apologise. You can always PM me here on the forums to order.