Well, the JS Enhancement Sling arrived a few days ago and was duly put to the test this evening under some light grey Kalenji lycra shorts.
The g-string style is quite comfortable and sits relatively low at the back. The front sling is very comfortable, but it doesn't give a huge lift. It is one size fits all, so maybe they could do with sizing it so that the fit is tighter and the lift more obvious.
With these fairly thin and very tight lycra shorts, not a lot is left to the imagination! I set off with a good semi and it all felt quite loose and bouncy at the front! I could feel my cock rubbing on my inner thigh which obviously you don't get with briefs or a thong on.
Overall 6/10. Comfortable, but not brilliant if it's an enhanced bulge you're after. That said, wearable without being outrageous but leaving little to the imagination, especially if it rains!