They are required by law since 12 December 2016 (actually earlier but it is most definite since then). There is however a (continuing) consulting period for ACM rules to clarify and synchronize the rules for all connection types which has not been concluded and offers them a 'way out'.

Though, if you have a SFP module you should be able to acquire the login details (through some googling, or https://community.t-mobile.nl/t-mobile-thuis-algemeen-490/gl...) and place the module in any SFP capable device of your choosing.