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cdru
It's well made - not cheap (both in quality and cost of materials) and amateurish
Works well - No fundamental design flaws that cause people to swear at it (or at least no more than any other design)
Works at basically any temperature - PLA, ABS, Polycarbonate, nylon, whatever you want, it's no the hot end that's going to be your limit
First commercially available all metal hot end - Not positive on this one, but I think it was. If it wasn't the first, it was one of the first
Cost - It's cheaper than other popular commercial all metal hot ends - the Prusa Nozzle and Pico - at least with the advertised pricing
Compatibility - works as a drop in replacement for many setups

JHead style hot ends are more popular, and they are cheaper. They also don't have as high of temperature range and can have a melt down. But at lower temps they don't require active cooling where the all metal hot ends usually do. There are many knockoff JHeads that are of....inferior quality or other design flaws that don't make them as good as the origianal JHead designs. They may work...they may not.