This is a cross between H. carnosa and H. serpens that is a very nice plant.  I find that its difficulty level is also a mix between the two – It is not nearly as easy to grow as carnosa, but not nearly as hard as serpens can be.  It was a plant that I had high expectations for, but it never quite lived up to them.  I do however still keep the plant and would encourage you to try it as well.  A well-grown ‘Mathilde’ can be quite spectacular when all in bloom!