In fairness to Uniden, they don't guarantee that a scanner will decode good audio from any system at any location. There are too many variables, especially with a handheld. The 436 performs according to its specs, it's your responsibility to determine if that is adequate for your particular purpose.
The thing is that simulcast isn't a problem everywhere within the simulcast coverage area. I monitor 3 simulcast systems with generally good results--I can hear them all with good decode in my house. Now if I drive around, reception quality will vary dramatically, there will be dead spots where one site or another is completely unreadable. Fortunately the systems I monitor have 2 or more simulcast sites, so in areas where one is unusable, I can almost always get good decode from the other site.
Not everyone lives in a simulcast area, and you can get decent audio decode in most simulcast coverage area with a x36. But they are obviously not perfect, and if the SDS100 can get good decode in 99% of the coverage area instead of ~70%, it's a big step forward.