That's the sort of question that can start a debate approaching the intensity of religion/politics.
Are there any downsides?
First - be aware that Jeep is a brand, like Suzuki, and there are many models in the line up, from the much vaunted Wrangler to the Fiat 500 based Renegade, each with it's advantages & disadvantages - you really can't compare one Suzuki model to an entire range - well you could, but it really wouldn't be a fair comparison.
Since most people think Wrangler when they think Jeep - I'll respond from that angle.
Because the Jeep has two live axles, it will have a significant advantage in most off-road situations, and on-road the Track-kick, with it's independent front suspension and live rear axle, will have the advantage of a smoother, more comfortable ride. The components that give Jeep the advantage off-road, are the same ones that become a disadvantage on-road.
The Jeeps are larger & heavier - you can decide if those are advantages or disadvantages, a decision which will vary based on the situation you're facing - a smaller, lighter vehicle can often go places where a larger, heavier one cannot, and they will typically burn less fuel doing it. Larger & heavier needs more power, stronger axles, and the list goes on, pretty much anything you can do with a Jeep, or to a Jeep, can be done with a Track-kick, but it becomes an endless cycle of build, drive, break, rinse, repeat.
In my mind, there is really only one advantage to owning a Jeep - there is better after market support - you can pretty much buy anything you want, off the shelf, and bolt/weld it on, with a Track-kick, you're going to end up doing your own fab work.