I quote from the letter that came with the product:
Your participation in the INNOVO product review programme also requires that you share your thoughts and experiences with the Gransnet community at the following times [ ...]
1. 4th-6th December, when you have been using the product for a full 4 weeks
2. 29th January-1st February, when you have finished your 12 week programme.
You will receive an email from Gransnet prompting you to give your feedback just before these time periods. [...]
It isn't mentioned in the letter, but at some stage we were also told that we would have to return the product if we didn't fulfil the requirements.