2013 WRX. I installed my Cobb short shifter last week. Very smooth and simple install, just make sure you have snap ring pliers. Other than that couldn't be happier. Installing this definitely tightened up my shifts. I'm not sure if that's how it was supposed to happen since I assumed your shifts tightened up only after doing the front/rear bushings. I guess not, and just installing the short shifter shortened the throw (as you would expect) but also made shifts a little more precise I would say. It did seem like shifting required slightly more "force" which is what I mean by the shifts tightened up. Not a bad thing, not like it makes shifting hard or anything, just tighter and shorter.
My front/rear Kartboy shifter bushings arrived today. I was excited and jumped right into installing. Definitely a little challenging having never done anything like this and only going off of the research I did with respect to installing videos and guides, but it can be done. The rear shifter bushing was by far the most challenging thing I've done yet on this car. I almost gave up and put the crappy OEM shifter bushing back on because I could not get both bolts threaded at the same time. It seems the holes on the bushing don't like up perfectly with the threads on the body of the car. I knew this ahead of time since so many people mentioned it in reviews of the product but I gave it the benefit of the doubt and went for it anyway. A couple hours later after literally wrestling with it from all possible angles, I got the second bolt to catch onto something. It seemed to screw in a little snug at first but wasn't too difficult and didn't get any harder to tighten so I'm hoping I didn't cross-thread the bolt. But it doesn't matter because I don't think I plan on ever changing that out again it was such a pain to do in the first place. I guess the manufacturer hasn't really taken customer feedback into account when continuing the production of it's rear shifter bushings; it just seems like this could easily be avoided by making the holes spaced apart further by like a millimeter. But I digress.
Only thing is, to my dismay, I didn't really notice much change in my shifts from installing the front/rear bushings in addition to the short shifter. There is maybe a slightly more pronounced gear "whine" in 1st and 2nd gear, which others have also mentioned. It is not really that much more noticeable from stock. I guess I was expecting even tighter and more precise shifts, but nothing really jumped out at me. If anything I guess I just upgraded to more quality bushings that will probably last much longer than the stock ones would have.