I've not tried Dexter beef, but Shetland is AMAZING
Rosemary is in Carnoustie and should have some to sell soon (she'll see this once her broadband's up and running again and get in touch I'm sure
or you could drop her a pm) I'm waiting for mine to come back from the butcher (it's another torturous 2 weeks to wait
) but I'm all the way down in Lanarkshire.
They're easy to keep (unless you get a mad, fence jumping heifer like I did
but she's not the norm for the breed at all) hardy, take little supplementary feeding and can out-winter if they really have to - although you'll enjoy keeping them and tending to them more if you can house them for at least part of the winter.
I've not kept or eaten Highland, but have been told it's a gamier meat. You've got the handling concerns - those horns are dangerous, even if the cattle don't mean them to be and I've been told that although they look big and beefy, the amount of hair they have actually covers a fairly scrawny frame (not my words - don't shoot the messenger
)
HTH
Karen