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Plum tomatoes are generally used for cooking, Vaca - not salads. The exception is if you have a "baby" variety; they tend to be sweeter, and are fine uncooked.
The normal cause of grittiness (as far as there is one) would be being under-ripe; that can make texture unpleasant. Perhaps try another variety next year, one that you know to do well locally?
For eating, I think one of the best is Sungold, which is orange when ripe.