I'll also recommend this option. If it's Refoss or Meross, it's the same thing. There's a non-HomeKit version too if that's not your thing.
Soldered the contact wires from the controller to the actual button contacts inside (Not the contacts that go to the opener. Same as OP did). The button connection to the opener doesn't change. This allows me to keep using the button as normal and the dry contacts that are built-into the Refoss/Meross controllers closes the actual button on the Chamberlin wall mount button module, so the encrypted signal is still sent to the garage door opener. As many are likely aware, you cannot just close the button connection points on the opener like in days of old. You need that encrypted signal from the wall mount button to be sent to the opener. I'm pretty sure the wires from the opener to the button are just power for the button. The actual connection to the opener is wireless. I recall having to do a sync proceedure after I reset everything. This opener was here when we bought the house, so I wanted to make sure that there weren't any wireless controllers not in our possession that were synced to our opener.
The wires you see coming out of the top of the Refoss controller are going to the included wired contact sensor and mounting bracket. This indicates the status of the door position. Simple and effective. The only other thing needed is a nearby outlet or other source for a 5v USB power connection for the Refoss/Meross controller.
You can of course mount it properly somehow. It's an oversight on their part not to have simply added some additonal plastic to the case with some holes for screw mounting it to a surface. I just happened to have a shelf that was already in the garage and the bottom of the shelf bracket was very accomidating to my laziness. Shoved it under the bracket 
For an iOS user, this is a really great addition and inexpensive. Very quick access your garage door from iOS control center, and if you have CarPlay, you can control your garage door from there too (appears once your CarPlay connected phone joins the WiFi network as you pull into your driveway).
