We have two Cairns at the moment, and had a singleton before them. All three came as adults from breeders, so their genetics were good but their training variable!
The singleton had had pups, and was our dog when ds was born. She hardly left my side from the last month of pregnancy and through maternity leave; I was never sure whether she was protecting us both from unknowable threats, or individually from each other! As ds became more mobile, she was gentle, patient and absolutely bomb proof - even when he tried to ride her and pulled her fur. (We did stop him immediately!)
The current dogs were wilder when we got them, having been outdoor dogs in a pack of 12. They are much more inclined to play with ds, who is now 9 (water guns are a special favourite) and can get a bit out of hand if he gets over excited. Again, never rough.
They do tend to be quite independant, and are very much better for careful obedience training as puppies. Bitches are brighter, and a lot more dominant. Dogs tend to be nice but a bit dim!
Cairns can be extremely effective escape artists, so good fencing is essential. They can also be very vocal - at its' worst this means they are excessively arfy, but they also vocalise - dog one used to yodel, and one of the current pair has a sort of singing rrroooo, which is charming. Terrier means 'earth dog' and they do dig, which need to be watched out for and controlled. They don't need a huge amount of exercise, being quite happy to race around the garden, but always appreciate a walk.
They do need to be brushed regularly, and clipped or stripped - ideally every 2-3 months. None of ours have had any allergies or skin problems.
They like people and are very companionable, loyal little dogs. We reckon you get a lot of dog for the size! We are most definitely hooked, and will probably have Cairns again. I am starting the campaign early to have a puppy next time though.