I have another plant, Mark, that is very similar as well. I have a couple of seedling from TL200 seed, and though they are only 2 years old, they seem to have the same long dark spines, so I'm pretty happy with it.
In Craig, M. halbingeri is described as being flattened, globular wolly at apex, and with several long thin hairs from the axils; radial spines to 25 5-7mm long, thin subulate, straight.....central spines 2, 5-6mm long, yellowish white brown at tip.
Flowers funnelform, sulphur yellow, paler margins....style white, 6 stigma lobes, and from the SE of Oaxaca state. The photo shown has rather longer spines but not as long as in my flowering plant.
The photos in Pilbeam show yellow and purple flowered plant, both with very obvious brown spines. He also says that Wolf broadened the description to allow for completely brown spines and both coloured flowers.
My plant doesn;t have sulphur yellow flowers, but I suppose that with such diferent flower colours, there could well be some intermediate shades.