I have too many lithium polymer batteries in my spares drawer to justify buying. I think they are easier to design into 3d prints and make more sleek projects with. The cylindrical cell and holder creates a size constraint for your projects. That constraint is not super convenient when used with circuit boards. If you get something like an ESP32 board that includes a batman chip, it is quite easy to find a lipo that fits in the same form factor and is very compact in my experience. I tend to make things over engineered to the point I don’t finish a lot of them though, so perhaps a cylindrical cell in a larger enclosure would get more projects completed.