Good news is that, no extension tube is required for infinity focus.
The image is sharp, no noticeable chromatic aberration at bright targets. I shall try again during day time.
I've also tried to add an extension tube to reduce the minimum focus distance, it works, however, the whole thing is getting too long to be used easily.
Next experiment would be to try it out on the sun with a Herschel Wedge, and also my Solarmax 40/BF10, and maybe also on the moon. The JMI NGF-S works very nicely together with the draw tube of the Borg, focusing is both rapid and accurate.
With a 2" nosepiece, the connection is firm and rigid.