Working various networks to operate ATAK on (among other things) is part of my daily job description. The type of network infrastructure required to use ATAK can vary significantly depending on your use case. Feel free to PM me if you don't want to disclose details here and I can likely give you some pointers. GoTenna is an option if you're looking for COTS purchases and fairly easy integration, however it will not provide constant coverage in the sense of running ATAK over commercial cellular or other similar wireless architectures. In my experience, GoTenna works decently for specific use cases in a small/defined area. For example, LEOs converging on an active shooter scenario or when conducting a raid. However, if you're looking for a fairly constant "net" that will maintain connectivity throughout a city/metropolitan area similar to an LMR rollout or similar, the infrastructure needs to be much more robust coverage wise.
Regarding iTAK, one of the major hurdles is that it's much more difficult to maintain at the organization level due to the restrictions that iOS places on how you can download and install apps, etc. Android is very flexible, as well as Windows for WinTAK.