I hate to reach into the layout with my hands during ops, so I use the Kadee under track magnets myself.
The thing to make them work, and I mean REALLY work, is to adjust ALL the couplers on every car and loco!
Use the graphite powder as well, as it will make a difference.
The most important thing to do, is to only use Kadee's!
I have tried a lot of couplers and not one other brand is better, especially when mixed......
Another thing to consider is to use "scale"-Kadee's, as they actually couple together better on curves.