Its a lot more complex than period tracking, and requires a higher level of trust.
The existence of free software has never been an insurmountable barrier to selling software.
People sell both hardware and software. From one of the sites another comment replying to me linked to: "Unless you have a health savings account or a flexible spending account, Mira is expensive. A basic starter kit retails at $199, which includes 10 LH and E3G wands, and then a resupply of those wands costs just under $60 per month with a subscription. If you want to go with the “Max” starter kit, which also includes PdG wands, the price goes up to $229 for the kit and $80 per month for the subscription."
