We keep a herd of 27 Shetlands on our small farm in NE Scotland.
The Shetlands are hardy - ours choose to stay outside in most weathers - they don't like 'horizontal' rain, that seesm to make them go indoors.
Our cows calve fairly easily and quickly. They make good mothers, having a plentiful supply of milk. The calves are lively and get up very quickly after birth - must say the heifers are better at this than the bull calves who are sometimes a bit slower on getting the idea if where the milk comes from.
The steers make excellent beef, finishing on grass/haywithout the need for expensive concentrates.
Shetlands will be OK on poor quality grazing - they'll eat all sorts -grass, rushes etc. They will need feeding in the winter. Up here, each cow eats around 5 large round bales of hay over the winter feeding season (Nov-end Apr).They have fairly large feet for a small cow and will probably poach wet ground less than larger continental breeds.
We have handling equipment - a crush and a homemade race - this allows for safe working for the Vet at TB and BVD testing time. Also makes it easy for us to apply wormer etc, and for feet trimming as necessary. We also have a tractor and front loader that can carry the large hay bales to the feed rings out in the fields.
One feature of Shetlands is their lovely curved horns - some people would be put off by the thought of having horned beasts. They are very careful with their horns - I have been poked gently by one of our cows who thought she wasn't getting her fair share of the carrots. Actually had more damage by one of the cows standing on my foot - thank heavens for steel toecaps...So we don't find the horns a problem, but then we're used to this breed having kept them since 2008.
I would advise going to see a few herds of the breeds of interest in your local area - talk to the breeders and see how they get on keeping the cattle in the conditions you are likely to meet. If you give me a rough idea of your locale, I'll provide you with the contact details of the rep for your area for the Shetland Cattle Breeders Association - see website here:
http://www.shetlandcattle.org.uk/Sue