Does look like a spider, but it only has 6 legs and 2 antennae, and the little mandibles. It does not have piercing sucking mouthparts, so I think it is probably a beneficial. I would monitor it carefully, but leave it be for now. Arachnids, even spider mites,which this is way too big to be, have 8 legs.
If it turns out not to be a beneficial, I would hit it with a good dose of insecticidal soap. Even if not soft bodied, the soapy spray blocks the spiracles and they can't breath.
My definition of insanity; trying to grow heirloom tomatoes in South Florida!