I have a proform treadmill (which is basically the same company) and it has physical buttons for speed/incline. they are really inexpensive (slightly over 1000 usd) and I had no issues with it for years.

As for the iFit, more interesting than control would be to connect to the iFit to read the speed/incline and broadcast it over ant+/BT to the garmin watch (you could probably mimic a footpod for speed, not sure how you would do the incline). I'm not aware of any other way to capture "climbing" on treadmill and its killing the OCD part of me that NPG on TP is always the same as average speed regardless of the incline.

Can you post the link to the thread you were referring to? couldn't find it. thanks