A Scottish straight cat is a Scottish Fold without the flat ears. So, what is the purpose of a Scottish Fold without folded ears? I think that that is a reasonable question because the distinguishing characteristic of the Scottish Fold is obviously the way the ears fold onto the cranium. Without that owl-lke characteristic you are, it seems to me, left with a standard looking cat that could be a random bred cat. This undermines the concept of adopting a purebred cat. I know cat breeders don’t want to hear that but, thinking aloud, it seems to be the long and the short of it.

You will see Scottish Straight cats for sale on Facebook, which, incidentally, is against their policies but that is another matter. Breeders of Scottish Fold cats will have Scottish Straight cats for sale and this is forced upon them. The do not do this by choice. It is a natural consequence of the process of breeding this particular cat. I’ll explain why as briefly as I can.
The gene that causes the folded ears is linked to certain physical abnormalities. It is a single dominant gene that causes these cartilage problems when it is present in “double strength” by which I mean in the homozygous condition. This happens when one Scottish Fold is mated with another Scottish Fold. Under this form of mating all the kittens have folded ears but they are also liable to suffer from two serious defects (1) a thickened tail caused by the fusing of the tail vertebrae and (2) thickened legs with cartilage growing around the paws making walking difficult.
Because of this genetic link to these abnormalities breeders can only mate Scottish Fold cats with non-folded cats. The kittens from this mating have “single strength” genes controlling this condition (heterozygous) and they are then free of these abnormalities. They also free of the folded ears, at least half of the litter is and these are the Scottish Straight cats that are for sale by Scottish Fold breeders.

But perhaps the point is this: except for the folded ears, the Scottish Fold is a pretty normal, standard looking domestic cat and therefore without these abnormal ears they look like normal cats were no distinguishing features. And as people buy purebred cats for their distinguishing features it seems to undermine the purpose of adopting these cats.
It would be more sense to adopt a rescue cat from a rescue centre. There are many handsome, indeed beautiful, rescue cats and rescue centres and when you do that you potentially save a life. When you adopt i.e. purchase a purebred cat from a breeder you potentially end the life of a rescue cat at a shelter. So there is always that background issue to consider and which must be in the equation when deciding what sort of cat to adopt.
However, there is some dispute, it seems to me, about the creation of homozygous Scottish Fold cats, at least according to Gloria Stephens in her book Legacy of the Cat. She writes: “Some breeders have different opinions as to inherited genetic problems connected with this breed. While some claim a Scottish Fold may be bred to another Scottish Fold with no trouble, others claim that serious defects may show up when the cat reaches the age of five years or older.”
That statement puts the cat among the pigeons! Some people enquire as to whether Scottish Straight cats are healthy. They should be for the reasons stated above by which I mean there should be no inherited health problems which plague the folded-eared cat.
As to the personality of Scottish Straight cats, this should be exactly the same as the folded-eared cats. Gloria Stephens said that they are hardy cats with a sweet disposition matched by their sweet exprression. She also writes that they have “tiny voices and are not exceptionally vocal. They adore human companionship and have a gentle way about them that endears them to their human companions.”
As to the difference between a Scottish Straight and a British Shorthair, they are different breeds of cat completely. Although they may look similar. They should not look that similar in my view because the British SH has quite a distinctive appearance with a shortened muzzle and a squarer face.
Below are some more articles about the Scottish Fold: