Nguyễn, thanks for your feedback! I think the device could be simple enough so as to sell at cost or for a small profit and still not be too expensive for patients and treatment centers. Charging a small price ($3 or less) for the app could also help to offset the cost of producing the device.
You're right, they would work well together! I conceived of BabyStream Pro thinking about data, records, and communication for mothers and doctors alike. I would certainly want BabyStream Pro to be able to connect to health monitors, like yours, of many varieties for ease of data collection. I'm not sure it's necessary to combine them just yet, but let's see what happens.