I must admit that, personally, even if I wanted plutonium, I would build EFF 4 reactors and simply scale out if I needed more.
But, really, if plutonium is required and EUs out are entirely secondary then there are two things that come into play:
* A "plutonium breeder" is a reactor that has lots of fuel rods. The space in a reactor is limited so you have only that much space for cooling components so you want the rods to be as inefficient as possible as efficient rods, in addition to more power, produce more heat.
* That said, manual fiddling with a reactor to change rods (correctly) is a pain. So homogeneous rods is an important consideration. If all the rods in the reactor are the same type it is quite easy to setup automatic extraction - using ME / EIO / Thermal Dynamics etc - of depleted rods, and insertion of new rods automatically.
On these fronts, the presented reactor is pleasingly inefficient, and has loads of fuel rods - 23 in fact. What I find less pleasing are the different rod types, which means the reactor cannot be automatically refueled, and manual refueling could be disastrously error prone.