The 13 gram aluminum J-Head Mk V has been tested and proven to work fine. While the only advantage is it's light weight, I am planning on making it available in the near future.
Many people have asked me if and/or when I will have 1.75mm hot-ends available again. While I was planning on producing the mini J-Heads, that was when the 3mm to 1.75mm conversions were a lot more involved than they are now. With the Mk V design, a conversion is a lot simpler than with the Mk IV design. As a result, I am planning on making Mk V-B 1.75mm conversions available in the very near future.