They are cheap and useful, but there are the following problems
for sensitizing the tiny things. The size of the board is relatively large. In addition, the final deliverables usually
become larger, because the base board requires various additional functions such as a charging circuit, clock, storage.
Moreover, each additional function has a connector.
As a result, it is actually difficult to develop a "smart" sensorized things. Another problem is a software for controlling
the deliverable from a smartphone. It is not easy to develop a sophisticated mobile application for each deliverable respectively.