When you're working as a FreeFlexer, you are doing so as an independent contractor. You don’t have an employer, but clients. This means that employee rules for non-EU/EEA students in the Netherlands, such as having a maximum of 16 working hours per week, do not apply to shifts on Temper.
Important: you don't need a work permit to work as a FreeFlexer, your client can't require it. Required residence permits or ID types are listed here.