I just put one in my 40b. it replaced a korrila 1, 2, and nano. moves everything nice and the corals look happier after a couple days of it running. I do not think 2 would be needed in my setup. Got the wireless so that another could be added if i ever get around to upgrading my tank.

I have been debating getting a korallia or a vortech for my RSM250..

Vortech seems to be the way to go...

What size should I get?

hahha now im having the wireless debate.
although something tells me with over 1000 gph flow at max, I should be OK in a 40 breeder with just 1 mp10.
where the best place to put it?
pointing from one side to the other?

go with the mp40ES and just dial down the flow. I had a mp20 full bore on a biocube 29 and my sps loved it. then you can always use it later if you upgrade

hmmm good poiint

Bought an MP10 for my 40 gallon breeder and currently have it sitting on the left pane of glass.
WOW what movement!
the anenome is flowing like never before, the xenia the same and the poor fish are all wondering what the hell's going on haha.