In flower at the end of last week when it was sunny - the flowers are closed shut these last few days.
Mammillaria krameri is one of the larger flowered forms of magnimamma. This plant came from Southfields nursery last year.
One of the things I was surprised at was the brightness of the flowers, as pictures I have seen on the web suggest white to pink not this deep red. I guess it could be a cultivar, and I know that flower colours vary a lot with this species.