No, your chance of starting a new variety of tomatoes that bares deformed fruit is slim. Probably the same as your regular tomato making a deformed fruit. Unusual, but not rare.
It does matter the seeds you save. Its matter on which plant donated the pollen to pollinate your plant. It is the same as humans we are all different when we come from different parents. In the case of tomatoes, if it donated it's own pollen or the same variety plant donated the pollen then you will get the same type of tomato as your plant. If it was pollinated by a different variety, what you get will be unique. You will be the only person growing that plant. If it self-pollinated, it had not different genetics to work with, so it basically creates a clone of itself.