I've got an MA3 for the rear on my fixed gear commuter and I've been very happy with it. My road bike, however, has Open Pros and those wheels have not been so great.

This almost certainly has more to do with the quality of the wheel build than the rims. I suppose it could have something to do with the fact that the Open Pro is on a wheel that had to be dished to accommodate a 9-speed cassette, whereas the MA3 did not, but I think it is more likely due to the wheel build. I built the MA3 wheel myself-- I'm not saying I'm particularly good at it, but I did it carefully and used the correct spoke tension. On the other hand, for the Open Pro wheel I bought it complete from the mail order company that had the cheapest price...I suppose it should be no surprise that it was laced poorly I've had several broken spokes and frequent truing. I've since retensioned the spokes and it seems to be holding up better.

My point is just that I think you're fine saving some cash on the rims-- just don't skimp on how the wheel is assembled (or do it yourself).