Think of most games with factions. You start with a factory with 3-4 units, you get a second or third each with 3-4, for a total of 9-12.
Each of our factories STARTS you with 9-12 units, and you can add in more by mixing in new factories over the course of the game, combining 2 or more 'factions' together.
I know of no games with as broad a starting unit lineup as we have. The only thing I could think to make this better is to broaden out the lineups of each factory so you don't feel that you absolutely 'must' change factory against an enemy tactic (say, getting anti-heavy from spider or jumpers vs a tank factory to make countering go from incredibly challenging to trivial).