Since tokens are harder to come by and are the main accepted currency now, there is a premium on these mana tokens. You will find it much easier to trade with these and you can go over 2b mana by owning these.

only question i have, since 2bil = 20fg, which 1bil = 10fg, which 200m = 2fg, how does 200m = 4fg

You really dont know about mana token. Mana token is 300m because of upgrades.

They just fixed the mana glitch so i don't see the point in owning one of these.

its to trade ingame and to go over the 2b cap

You pay extra for convenience, the best comparison I can make is silver Bullion. Regular Silver bullion usually sells for right around spot price just like normal mana. While mana tokens are like American eagle silver ounces which sell for a premium because people are familiar with them and are the preferred way of owning silver.