IMO X-outs and Factory Seconds are totally worth it, especially if you are just trying to get a handle on a mold you've never tossed around before. I have owned quite a bit. Most of these X-outs or FSs have obvious blems, such as minor specs of another color in the plastic, bubbles in the rim, or maybe just a bad stamp job. Whatever the case, most of them fly true to what they are designed to do.
Every once in a while you might come across one that might be slightly different than the actual mold, but I think its more with the domeyness of the disc, which will affect its stability slightly. But I don't think there's anything wrong with that. If anything it might give you a little something different out of a mold you are comfortable with.
All in all I think the X-outs and Factory Seconds are a great deal. Especially when starting off. You will just have to get a bit familiar with the different names of molds and their abbreviations. They should always have this in the center of the underside of the disc...along with the ink pen "X" in the center of the top of the flight plate.