They were my first breed

Beautiful, elegant sheep. I found them perfectly easy to tame, no harder to manage than any other primitive type. (Which generally have more brains and independence of spirit than many more commercial, softer types

)
Fanatastic meat, lean but not dry, incredible flavour. People who don’t like lamb like it - as do those who do

Slow to mature, less meat on one than a Shetland.
If you are interested in spinning, take great care in selecting your stock. In recovering the breed from the brink of extinction, the focus was taken off the fleece and they are really very variable now. The standard calls for no kemp, a very fine fibre, not too long. You will find kempy Castlemilks, I regret to say.

. You will find ones with very fine, highly crimped fleece barely an inch long, and ones with soft but less fine and crimpy fleece with a staple length of nearly 4” in places.
Many Castlemilks will roo their fleece, which may make them unsuitable if you want to use the fleece.
I had two females, not bought from any well-known breeder, so my experience may well be unrepresentative, but mine were not the best breeders in my flock. If it was important to me to produce numbers of lambs, I would probably not use Castlemilks. But if I wanted beautiful sheep that are a pleasure to own, lovely meat, and maybe some amazing fibre to spin, then by all means yes.