Its not the runners that crack, its the wastegate flange. I used this same manifold but welded the wastegate flange to the turbo flange. I also added a second heavy duty brace from the head flange to the turbo flange. Used it for a year with no issues with it cracking.
As far as fitment, unless your willing to go to a half width civic radiator and possibly notch the upper radiator support, forget about running it. As far as flow goes, it definitely flowed well enough to make good power without having backpressure issues. This manifold will outflow a log manifold period, end of story but again its meant for RWD and its cheap so dont expect it to last forever.