a few "grafted" ones - have you tried these,
I haven't had the need!
I can't really see the point of them unless they are something that is a bit special and needs a stronger root stock to increase the amount and or size of the fruit.
If this be the case I don't think I will bother, all I want is a good crop of nice tasting tomatoes and I get these from the seeds I save.
I suppose another reason is; I am not a connoisseur of tomatoes, perhaps I am too easily pleased!
Dull isn't it 8)