I need to store a record of lessons members have read (viewed for more than 30 seconds). I would just be a list of date/time and lesson number. It seems excessive to create an 'achievement' for each one, a member could end up with hundreds of 'achievements. Is achievements the appropriate service or should I use another.
PS. I did look at 'storing additional information with 'user' but the js for that isn't written yet anyway.