Using seeds from supermarket tomatoes

My advice would be not to rely on just the seeds "harvested" from fruit that you enjoyed eating.

You are going to spend 3 or 4 months growing that until you get a harvest which may, or may not, be tasty. If its not tasty, and you decide to rip the plants out, then if you have planted some other, "known good", varieties you will have a fall-back crop.

If they do come "true" then you can keep the seed from them for future years and, chances are, that will come true too.

I grow some Buttternut Squash from seed that a friend gave me years ago. They are outstanding (even if I say so myself!), and I save seed for the following year. But I always grow A.N.Other variety from bought seed just in case mine don't work. (this year I have only managed to grow one viable seedling but its also possible that they will be cross pollinated and come up half-squash and half-courgette or somesuch!!, the Squash/Pumpkin family are notoriously promiscuous).

But for the last few years, at least, I have wound up giving away the fruit from the stand-ins