PS - they'll suck the maintenance resources when you overhaul them. Overhaul uses maintenance at a multiplied rate - I think it's 4x to match the rate at which the clock unwinds. TANSTAAFL
Actually, I don't think so.
Currently, my 20 Chimeras are using 379 duranium per year at my maintenance.
At the current time of posting, the last three chimeras to be built have just finished their overhaul.
The production window still says 379 duranium per year.