imo these are two completely different animals.

D300 doesnt need a separate power supply, but could use one if you wanted more wattage. Has smart feature, but low discharge rate. Awesome overall footprint though.

4512 charger itself is way bigger, and needs a separate powersupply. But is capable of more than 5 times the max capable wattage of the D300. Easier access between the two channels.

If I don't feel like digging out a bunch of stuff, D300.
The D300 and FD200 discharger both still take up less space than my other charger setups overall.

If I need more power, both for charging and discharging I use my other chargers. Using the Icharger is a little quicker with the spin wheel and separate channel buttons.

Smart charge feature of the D300 seems like a very cool feature, but I've yet to use it. Reminds me of the bump tags that my powerlab charger uses. But became obsolete after the company tanked.

And for the smart charge feature, your limited to specific batteries to use with that charger.

Finally, PRICE. You could easily buy seven D300's for the cost of this Icharger setup. Both are awesome, but not so comparable to one another.