Ordinary chain link connectors require a special tool for it to unlink the chain. I have never tried to unlink a chain using this method, but I hear it is quite burdensome.
Allegedly, the Wippermann Connex Link makes unlinking the chain easier. Hence, I bought one in Flying Ball last March for HK$65 (PhP360 or US$8).
The product is really small. It's about half an inch long. It's way smaller than the box it comes with. And the only reason why the box is bigger is to accommodate the instructions. Mang Nestor, the Brompton expert in Tryon, didn't even bother to read the legal sized document. The guy knew how to install this link. So, I let him be.
Anyway, after Mang Nestor installed it, that's the link (inside the blue circle). With the Connex installed, it's supposed to be easier to find, and quicker to unlink the chain. No need for the special tool.
PS: Apparently, there are different links for different chains (10-speed, 9-speed, 8-speed, etc.). For my Brompton, I got the 8-speed. Please talk with your LBS' mechanic before purchasing one.