I’ve used odoo before, it is a large piece of software and can be modified to do lots of things. Most likely you will be able to get it to do what you want. You’ll probably need the e-commerce module, there is probably some sort of mode for subscriptions. You can also add the CRM on top for marketing, etc. there is also the booking module (iirc) which is maybe useful for sessions with trainers etc. maintenance might also be useful.
What is the purpose of the device? I’m almost certain that there is another option, which is just a small PC running whatever software you need.