After receiving permission to post his e-mail, here it is:
I've been using your J-head hot end for a few days now. For what its worth, here is my input: Huge kudos for having it pre-assembled. Probably the only issue I had with hybrid insulators is getting the PTFE to brass junction tight but not too tight. It either allowed a plug to form or I was clamping down on the filament via over-compressed PTFE. All I had to do here was install a resistor and thermistor. That was pretty cool. My past experience with resistor based heaters has not been too great. They always burned out after a couple of weeks. Yours is a bit different from what I had been using, so maybe it holds up better. It fits much more snugly too, so it should dissipate the heat better. I'm really interested in seeing what kind of lifespan it gets. If it only lasts as long as my other resistors, I'll probably be hunting for a heater cartridge to replace it or at the very least finding a way to wrap nichrome around the heater block. The PTFE insert has been a really awesome improvement so far. Again, I'm not sure what to expect as far as life span but yesterday I wanted to use a new groove mount holder. Normally I would have had to heat up the filament before it would back out. Without even really meaning to, the cold plug actually popped out while I was changing the holder piece. I thought that was a pretty impressive display of the difference in friction. I'm not sure if the camera really captured it well, but I thought it was impressive enough that I took a picture of it. I assume this has to do with the fact that the PTFE feeds further into the hot end than normal? The tip on this hot end is much more blunt than what I have seen before. I'm not sure yet if this is a good or a bad thing. In theory, as the extrusion is pressed flat, the wider tip would keep it more evenly pressed flat against the previous layer. This presumably would lead to better layer adhesion. However, I had a lot of difficulty yesterday printing a 110mm fan cover. There was just a hair too much plastic being extruded, I think my Z endstop slipped a little and let the extruder drop lower than normal which caused the extrusion to widen out too much. After a while, little balls of excess plastic started forming. My other extruder tip would have plowed right through them no problem, but the wider tip on this one seemed to snag more and eventually caused skipped steps. Extruder tips with a sharp cone point seem to handle plowing through excess plastic better which makes it less difficult to reach "usable" printer settings.