While correctly located slots on any given body tube will locate the fins correctly about the circumference of the tube, they will not insure that the fins are radially correct. There has to be some slack in these slots in order for the fin to be inserted and because of this slack the fin can deviate slightly from theoretical "perfect". The resulting deviation is most apparent on four, six, eight and other even numbered fin configurations because these also need to be on plane 180 degrees opposite another fin, just as the OP's photo shows. It's much harder to see any deviation in radial alignment with odd numbered fins, 3,5, 7 and so on.
That is the beauty of my little contraption...it not only holds the fin in position while the glue sets, it adjusts for tube diameter, fin thickness and fin alignment in both the longitudinal and radial axis. Even so, one should still do a visual check, especially on even numbered fin configurations. (End of shameless plug)
