Comments about JTL JTL Angle-Adjustable Adapter with Umbrella Holder for Lightstands.:
In general, I'm happy with this holder. While it is not metal it is strong enough to hold 10-15lb (my estimation).
The only problem I have - the top mounting screw is located too close to the umbrella hole. As result, after umbrella is installed you can not rotate the screw. Not big problem - just install umbrella after the light - but could be designed better.
Comments about JTL JTL Angle-Adjustable Adapter with Umbrella Holder for Lightstands.:
This doesn't come with a stud for your flash. The angle knob it hard to tighten enought to hold an umbrella. Get this on instead http://www.adorama.com/SPSB.html . It comes with 2 studs, a large handle to tighten the knuckle and is [$] less!