Cheapest I could find for 6 pcs - shipped direct from China - Arrived within 10 days via Post and Work!
The Units are fairly light so don't add much weight to the new LED bulbs I installed.
Construction: Lightweight (Cheapish) materials, Edison Screw made of pretty light low grade 'alloy'
Ceramic/plastic holder is light but seems sufficient to hold the bulbs securely, however I was careful not to over tighten
as I was not fully confident they would not crack with too much force.
These converters give you an ideal way to use GU10 LED Bulbs which along with MR16 seems the most easily available type of LED available. I have however also seen similar converters to allow use of SES and BC type bulbs but more usefully for the UK, converters for standard Bayonet lamp fittings to GU10 Bulbs.
For the money I cannot fault these.