I'm on a project that requires flashing ~20 ESP boards. The thought of needing to solder that many 4-pin headers was really worrying me. I searched around online and discovered Pogo Pins, then spent some time seeing if I could find any pre-made solutions for my 4-pin header. I eventually found PogoProg. Item arrived in about a week. The side-mounted pins and the rounded shape make it very easy to hold and use. I need to be able to keep in place for about 20 minutes per device, so I made up a simple jig to keep it held and tensioned. So far the device is working great and I'm thrilled to save all that soldering.
I had a question about my order so contacted the seller. I got a quick reply and was very happy with the whole experience. I would definitely consider purchasing from this seller again in the future.
Getting it writing for the first time was a bit frustrating. Had to update the windows device driver to the latest BMP one. After that it was smooth. Works as advertised. Have used it for a few nRF51 projects.