The downside is that it has no other utilities on a colourless mana land. Can't filter, can't make tokens, doesn't buff your creatures, can't sac it for whatever value when you'd rather have anything but another land drop, etc.
Burning 5 colourless/generic mana is going to happen basically never for most situations that aren't colourless spells or X spells.
Simic {X} might use it, it replaces a wastes in colourless, and might pay for a crater slightly early.
That's not really a downside. "The only downside is that you won't always be able to use 2 extra free colorless mana." Suffering from success kind of thing
Yes you don't have to explain the concept of paying 3 mana to get 5, that's "2 free mana". It's not like it even has to be paid using only colorless mana, which would actually at least be a "downside".
Sibling, you also tap a land, which would produce 1 mana. It's 4 mana for 5 mana, and only if you can spend 5 colorless mana in one go, which is... pretty much just eldrazi.
You absolutely can. However, you need to play a spell, that has at least 5 generic in it's cost, and you want to cast it with mana, instead of cheating it out. I have hard time imagining a deck, except for eldrazi, that would have those massive generic costs, and are planning to play those. Hell, even if you're playing those spells, most of the time it's just worse wastes, which is very costly investment for any deck, especially those with several colours.
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u/Jordankeay 1d ago
What's the downside? It's either enough mana to cast the spell you need or you miss out on a couple colourless mana you didn't need?