I saw some reviews that claimed this product did not always uncouple correctly consistently. My experience with it has shown that the Marklin 3000, the switcher loco that comes with starter sets, is the only loco that has an issue. That loco only has a simple hook instead of a coupler, so it's the loco and not the decoupler that causes a problem. The car coupler simply goes back over the hook when you try to uncouple them. You can overcome it by moving the loco forward slowly while engaging the decoupler. I have had almost 100% success with every other car or loco. It is very loud, especially if you are holding down the switch while moving the 3000, but I really don't care about that. It works way better than I expected. You don't have to be perfect where you stop but centering the cars over the decoupler helps a great deal as expected. It also has a manual tab to push for those who don't have electric accessories.
The uncoupler works great on Marklin and Liliput rolling stock. Great advantage of the light is the ability to position the train for uncoupling of cars when at a location away from the transformers but still in your line of sight. Also the light makes is easy to tell when the uncoupler is being activated.