In-ground round trampolines are great if you have a scenic view you wish to protect from the obstruction that a safety net can be, or you live in a high wind area and want to further minimize the risk of a trampoline blowing away.
Often round trampolines are installed in-ground to repurpose a pool or pond hole.
We are aware of the number of kids who are into running and flipping on and off objects freely in the name of Parkour and free running; they want an in-ground trampoline but installed above the ground so they can run and jump on and off it. For everyone else, we do strongly recommend although the design of the GeeTramp has legs, to install the in-ground trampoline in the ground in a purpose-designed hole with retaining walls and drainage.
Be aware that typically installing an in-ground round trampoline is a little trickier than a rectangle one - from what I've been told - I've not ever installed one.
If you decide to use an in-ground trampoline above ground be aware of the risk of injury and the severity of it does increase off trampolines without nets.
Why GeeTramp In-Ground Trampolines have legs.