If you really like a figure don't let the size deter you. Buy the Commander figure you like. You don't have to buy them all(though they do become addictive).
I prefer the smaller Tf. I can collect an entire line and don't have to dedicate massive space for it. Larger figs have their bonuses too though with articulation. The DOTM Commanders are also longer in alt mode than say Deluxe Optimus.
DOTM Prime is good, Prime:RID Optimus looks great.
Point is, $10 for a Commander is a little high it seems, but like you said, they are G.I. Joe size and those cost $7-$8.00 anyway. You pay an extra 2 dollars and it's like you get 2 toys.