The tracker does have arrow keys and they work as you would expect them to - look on the lower right side of the unit. In general, most things have their (semi-)dedicated keys, so it’s surprisingly close to navigating a classic tracker with a computer keyboard (source: used various trackers since I was 12, I’m now 37).
The grid is mainly used for fast input of notes (you can also change note value with the encoder) and parameters as the grid values map from minimum to maximum value so if you know the value you want, you can whack it directly from grid (this can also be done with the encoder). All the navigation is done via the dedicated mode and navication keys, and there isn’t much you really need the grid for if you’re more comfortable setting values with the encoder.