They are a bit , but as I was needing 2 heads I went for this as it also had the controller all in one pack , other heads I'd priced were going to cost the same and still required a controller on top .
The turn over for my tank with sump pump flow (-losses) included is about 50x/ hr total when all running at once.
Having more heads can help eliminate dead spots in the tank which which means more detritus in the water column which in turn means it then has the ability to go down the overflow and be filtered out .
Quote from page above :
High flow (40x-100x+):
Some of the low and medium flow corals will do ok if placed out of direct flow up past the 50x turnover mark. Corals from the medium flow group such as: xenia and leathers will still thrive in high flow. Fleshy LPS will have to be placed in a relatively dead spot to survive in a high flow aquarium. 50x+ turnover introduces a whole new group of corals known as small polyp stony (SPS). SPS coral needs very high flow to keep its polyps clear of waste.
The amount of flow is dependent on what you plan to keep ?, I'd like a mixed reef so have gone for 50x flow .
One of the 10000 l/hr pumps added to say a 4000/5000 litre return pump (minus losses) give you 50x flow but the power heads may be better split two 5000 l/hr pumps to give better distribution of flow as opposed to all from the one place .