I’ve converted my two MTH O scale boxcars and my Lionel Legacy SW1 locomotive from the standard Lionel couplers to Kadee couplers. The Kadee couplers are much closer to scale size, and couple together very easily at slow speeds. Further, by body-mounting the couplers, I should have somewhat better reliability when pushing cars through S-curves and other complicated track work areas.
The conversion to Kadee couplers isn’t hard, and is actually quite easy with the SW1 locomotive, but is more involved with the MTH boxcars. A large number or screws had to be removed to take off the existing couplers, a bit of metal trimmed off the trucks so they wouldn’t be limited in how far they could turn (as they would otherwise contact the coupler boxes), and I needed three different screw sizes (well when including the screws for the SW1). Nothing was hard about the conversion on the boxcars, but with all the screws to remove it did take a bit of time. However, the second coversion only took me about 5-10 minutes since I knew what I had to do at that point.
You can watch the video below to see how I did the conversion. This conversion doesn’t make a lot of sense if you just want to watch trains run and don’t care about the appearance of the couplers. But, if you enjoy slow switching operations and want a more proto-typical look to your rolling stock, you might give the Kadee couplers a try.