So, I dug some of these up, yesterday (just for one spot of plants, and those that grew into them from other plants). I discovered that the tubers extended about two feet away from the plant! I got a few that were a fair size, too.
I baked them like potatoes and tasted them. I was amazed and impressed! They taste totally awesome! They're like a mix between already salted and buttered baked potatoes, fried potatoes, steamed cauliflower, and some sort of seafood. The skins even taste really good (please don't peel them). They were so good that I ate a whole bunch of them, even knowing that the inulin content might give me gas. It did give me gas for a few hours, but it was worth it (although I recommend being more conservative than I was)! They were white inside, like moist baked russets. They get quite soft when baked sufficiently (and that's how I recommend them: soft). They were about the color of russets on the outside, too (the ones I dug up weren't red or purple, but I found a few shapes; some where kind of like chicken feet, some were really long, some were maybe like fingerling potatoes, and some were short and fat).
I was surprised at how salty and buttery they tasted. I wonder if they have extra salt tolerance.
Yes, even the long ones taste great (you can eat the whole thing, skin and all).