The founder of Allestoringen sold it to Ookla in 2018 [1]. It seems they do have an enterprise offering these days [2].

Re: banks, there is also the iDEAL status page [3].

[1] https://tweakers.net/nieuws/142053/storingswebsite-allestori...

[2] https://downdetector.com/enterprise/

[3] https://beschikbaarheid.ideal.nl/