Hi Andrea,
If you want something very portable and convenient, I would say iPad Pro (models from 2020 with LiDAR). The iPad is less expensive than iPhone12-13 Pro. RTAB-Map for iOS is available on AppStore, but there are also many scanning apps there to match the application you need.
K4A is great alone, you may use rtabmap for odometry too (and even in
pitch black without lights). However, if you need the robustness of a tightly coupled VIO approach, there are indeed less choices. Are you using the RTAB-Map standalone app? or with ROS? With ROS you could find a VIO approach that could work with K4A to feed to rtabmap. There are also some VIO approaches that can be built in RTAB-Map standalone that could work with K4A (though not tested myself).
For ZED, I think CUDA is required to get the pose, but you could ask them on their github. They have an
open driver without CUDA, but we can get only the raw sensor data.
cheers,
Mathieu