I am actually at 3 x mp40. Here's my opinion so far....
- I have two on one end and two on the other end. I am considering moving one to the back and having it fire forward, but with my lift system, there are a number of obstructions to putting it on the back.
- Controllable from the Neptune Apex. Very nice.
- No extra drilling for a closed loop. Big plus for me.
- No wires in the tank OR over the top of the tank. This has been a huge plus with my lift system as I don't have to worry about cables issues with that and can still keep a tight seal on the tank with the canopy. No jumpers...
- Flow. Overall it seems pretty good, but not being able to 'direct' it is a downside for me. I think there are 'pockets' around the bigger live rock structure that will collect detritus. Some areas in the tank are not quite as high of a flow rate as I'd like.
I'm going to continue to work on adjusting position, settings, etc. on the pumps over time to see if I can improve it. I was also going to try and get on the Ecotech forum and see if I could get some inputs to improve the overall performance. I may need to replace the wet sides on two of them (all were bought used on RC). I did that to one that had a problem and it works much better now. That may improve flow on the other two as well.
Overall they are great pumps. Expensive, but still a reasonable option for flow. If I had to do it over again, I'd probably buy new pumps. The price difference doesn't warrant buying used when the new wet side makes such a difference.
My 2 cents.... Hope that helps.