Whether it's a good substitute or not depends on why you eat peanut butter. It has most of the fat removed. Peanut oil is high in healthy fats, so you're losing that benefit. If you get plenty of monounsaturated fat from other sources, then you don't need the extra from the peanuts. If you don't eat much in the way of olive oil, avocado, other nuts, and so on, then regular peanut butter is an easy, inexpensive way to get the healthy fats.
Many of the powdered peanut products add quite a lot of sugar to replace the fat, so watch out for that. You can buy partially defatted peanut flour (which is essentially the same as PB2 without the sweetener) for about 1/4 what the jars would cost. (Actually, about 1/6 the price you quoted.)
I've used both. Regular peanut butter (and other nuts) is one of my principal sources of healthy fat. Peanut flour is good when you want a strong peanut flavor-- to replace some of the flour in peanut butter flavored baked goods, for example, or as a base for peanut sauces or soups. I personally don't like the taste of PB2 or its imitators as a substitute for peanut butter. On its own, it tastes stale to me. But everyone has their own preferences, and a lot of people swear by it.
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