Most, if not all, tiny modules are designed with compromises. They usually have two options: more I/O and hard to solder, or fewer I/O and easier to solder. The BLYST Nano, on the other hand, is design to be easy to solder without compromising I/O. The video below shows how easily you can hand solder it on the breakout board.
Not only is the BLYST Nano made for easy hand soldering, it's designed for easy prototyping. The module contains all the required components needed to operate without needing to solder it on a PCB. It's fully self-contained. And, unlike most modules with under pads, the BLYST Nano PCB is made with high TG (heat resistance) so you can solder wire directly to the pads without lifting it. If you are handy enough, just directly solder the 4 wire VCC, GND, SWDIO, SWDCLK to hookup to a JTAG, the IDAP-Link for instance, and you're ready to flash the firmware and run.