I have stated very clearly that this play is a loss of tempo up front and that the math will smooth out if you graph it. At the start of the game you get 10 extra mana, how you spend it early in the game will guide your play style. If you play mana boosters up front with your extra mana, they pay for themselves as discussed. After many games with many different openings, I have found great value in the amount mana I am channeling in each turn. So much so that it isn't a simple (Casting Cost - 1 )/5 for the Crystal or Flower. The value to is provided by the enhanced channeling rate early and mid-game, basically rounds 2-8. I favor playing creatures in the 11-13 mana range. The straight channeling increase provides me the ability to summon a creature each round early game and allows me to use this mana to cast other spells in conjunction along way.
I think what others are disagreeing with is the idea that this channeling is a unique benefit from the mana generators. After all, if you saved the 5 mana that you would have used to cast the flower, you could instead dole that out over the next five turns, which would be equivalent.
Of course, this would obviously be pointless, since then you would be in the same position 5 turns later, but without a flower. So saving the mana-per-turn isn't the point here, saving the quick action and mana during the intervening turns is. When you talk about the additional channeling each round, you are correct insofar as there is no benefit to saving the 5 mana to use one at a time over those 5 rounds as opposed to casting the flower, if you are only using one of those mana per round.
If your strategy calls for investing actions in creatures, one per turn, then since you have a limited number of full actions (one per turn, coincidentally), it makes sense to ensure that you channel enough mana each turn to do that. And if your creatures happen to be in the 11-12 range, and you are not playing with a spawnpoint, then you might as well spend your initial starting mana to create mana generators, since you don't have the actions to do anything else.
But it is not correct to say that the channeling gives a unique benefit
during the turns it takes to pay off the mana cost of the generator. Playing the generator might be a no-brainer if you have nothing else to do with the mana and don't need more mana to summon creatures than you can channel, but although it undoubtedly gives you an advantage after it has paid off it does not give you a unique advantage while it is paying off; at best, during that time period, it is no better than simply saving your mana, except in the uncommon case when your opponent uses mana drain a lot early game. And the inflexibility that it gives for those five rounds (in case you need to cast something more expensive) is a downside during that time.