Wheatgrass leaves me underwhelmed. The health claims for wheatgrass have been wildly exaggerated, here is a good comparison of wheatgrass, broccoli and spinach. And a single ounce of wheatgrass contains 16g of carbs, 8g fiber and when juiced, you need to assume that all those fiber carbs are diced up and become simple carbs. And the recommended serving for an adult from the company you cite is 2-4 oz/day, that adds up to a whopping 32-64 g of carbs/day. And even when purchased in volume, it would cost $2.5-5/day to supplement.
I'm going to stick with my regular whole veggies.