This is silly and reductive. You make different design for manufacturing choices at different steps of product development and volume. In some cases, you may l

This is silly and reductive. You make different design for manufacturing choices at different steps of product development and volume. In some cases, you may luck out and find that a widely available dev board is actually a really good match for your needs, in which case, run with it. You'll cut out a lot of NRE and get your product in customers hands faster. Once you've shown that you can sell in volume, do a DFM pass for V2 to minimize cost. OP probably fits this case, as all they need is Wi-Fi and Bluetooth, depending on their eventual power solution. If you find that you're taking a dev board and soldering a lot of extra components to it, then I agree, you want to move to a custom PCB before doing any real volume. But you still might make a dozen first cuts with this and a 3d printed case to see how some product beta testers respond.