The best time to harvest shelly beans is when the pod becomes limp, especially on the stem end. Most beans will shell easily in that stage. The seeds within are fully mature... you could even dry them for next year's seed, if rain threatens. You can cook the shellies directly; but I prefer to blanch them first, then either freeze them, or resume cooking until tender. You get less breakage that way, and a little less gas too.
The shellies from Fortex are nothing special, and I've never tried shellies from Northeaster... but if you have a lot of them, better to cook them than let them go to waste. I like them seasoned with butter, salt, and either celery salt or basil. They are much better when the beans have had time to absorb the spices.
If you are close to getting dry seed for Fortex, take advantage of it; Fortex takes a loooonnnggg time to go from snap stage to dry.