I have both, motorized flat treadmill (commercial grade with no tech) and a curved self powered treadmill. There are pros and cons to both, but the flat treadmill is the most versatile.
The curved treadmill requires more effort to run on, so it is more of a grind to run for over an hour. But it requires no maintenance, just jump on and go. It is amazing for and my go to for interval running. You get up to speed quickly and can stop quickly. Trying to run 20 x 1' on a flat treadmill is difficult, you either jump on and off or have to wait a lengthy time for the belt to accel/decel. But doing longer tempo runs on the curved treadmill can be exhausting. It can also load up your calf muscles a lot with excessive use.
For me I love having both, they are a fantastic pair to cover all types of workouts. But, if I was wiser I should have just gone for the very expensive motorized slated treadmill that can do everything and not need any regular maintenance (my flat treadmill I'm cleaning and lubing every month, an annoying but necessary process). If I had to just choose one, I would hands down get the commercial grade flat treadmill. I like the curved, but only as a supplement to the flat.
The Wahoo Kickr looks really interesting though, it seems to have some great new features.