I would not exclude the possibility that it is M. hahniana (or possibly the related M. albata). In general, M. formosa (or chionocephala) has somewhat more brownish spines than the plant of the photo. And I have not yet seen a dichotomously dividing formosa, although I will not exclude that it might be possible.
Also, the presence of hairs seems to point towards M. hahniana.
If you look at M. hahniana on Maurillio's pages of the website, then you will see M. hahniana WTH845, which looks very much like your plant. I even found a dichotomous WTH 845, also shown on that page.
What is the flower colour? If it is reddish, then that would be a atrong indication for hahniana.
Wolter ten Hoeve.