As one reviewer stated on Dave's Garden, "Overall, this plant is only for cactus experts and/or masochists."
I know I'm not the former, and I hope I'm not the latter, but I haven't found this cactus to be too difficult. On the other hand, the reviewer is right - the hooked spines of Mammillaria senilis are ferocious.
But the blooms! Those big, glossy pink blooms!