If your cube is fast, e.g., Ismaru, hound of konda with Rancor then 3 real mana is probably already expensive enough. Leaving 4 mana up is a really a lot, but fair. Leaving 3 mana open already signals that trouble is up. The only time it is painful is when your opponent could not do anything and left the mana open anyhow.What sort of instant speed removal do you think is the right level? Something like commit // memory?
I like them a lot. Do not forgetHow do people feel about instantments? I've been happy with in particular. Granted they mostly get played in instant mode.