First: it creates a widget so for horizontal menu you need to have horizontal widget in your theme above, otherwise this plugin is trash.
Second: authors of the plugin links us to the info on how to create such widget if it hasn't existed: however, info is not fully accurate, many things don't check out (there is no parts of code they claim it had to exists) with the current theme I use and there is no clear description where to put the code exactly to make it work so I had to experiment a lot - took time, got it finally working with some error as to widget.php (about this there is no help in this hint, so we need to deal on our own with it).
Third: I finally had needed widget area but it was above all elements and menu in that place looked like crap and was not within theme borders. I am sure there is a way to customize it with further php coding. Don't know it? Forget about making it work easily :/.
Fourth: Ii all has no sense if there is no way to turn off original or custom theme menu. How to do it? Dig further... No easy way out here too.
To sum it up: plugin options alone seem to be very intuitive and nice, however this is widget based menu plugin so without php knowledge it probably won't work well on many modern themes where there is no proper widget area. I am using Andrina Lite and it was above my skills to use it. I tried, I make some of things working but I was nowhere near to have anything useful. So at the end plugin wasn't useable, unless I wanted to create vertical menu.