Well, the first three cards in this set are commonly known at least. Maybe not the last one, but I believe that it's part of the set. I mean, the other three cards produce exactly 7 mana so why shouldn't it be considered part of the set? Anyway, on to the actual set. The first three parts are really good, but the last one isn't that great. Albeit that the Factory can be used in the late game (or if you have the other three parts). Still, I like the set as a whole. It produces a huge amount of mana for very little. Now, only if there were a card that altered a nonbasic land type...
Pros: Large amount of mana for very little investment, entire set can make tokens in colourless
Cons: Requires set for huge mana output, only produces colourless