Just wanted to add our experiences with HLC. Like other might already have said, large HLC (or UPB) installations REQUIRES a phase REPEATER (not the phase splitter).
We have successful HLC systems that runs hundreds of loads without any real issues.
We have had even better success and stability when we used UPStart to acutally enroll the UPB phase repeater in the actual HLC network with the right ID, password and an available UNIT id on the HAI system. Strangely, even with the HAI phase repeater model, the Omni controller cannot add it to the HLC network and reports it as an unknown device. UPStart solve this problem.
It seems repeaters can be installed without configuring it but we found that when we do actually integrate them to the HLC network properly, the system is even more reactive and stable.
The "only" real issue we got is that if two or more user tap dimmer rockers at the same time, it creates collisions on the UPB network resulting in a false feedback lighting status on the Omni controller.
If you base some logic based on load status, your logic might not work. So if two lights are already on and two user close two lights at the same time, the Omni will not receive the status of the light level correctly on both dimmer or maybe just miss one status. If you had a logic condition that was for example "when door not ready, if light off, then light on" won't be executed because even though the light is physically off, the status is still on the Omni controller because of communication collision.
Other than that, HLC is working really nice, 32 rooms with 7 loads and 1 room controller for each room (32nd room only has one load), feedback works ok where there is no collision, system is reactive with maybe 1 second delay.
Programming is also quite fast and eazy for the installer and user. Install all dimmer/switches/scene switchs, fill up all the lighting zone and loads names in PC access, take your laptop with wifi and enroll all HLC devices one by one. Setting a scene is super eazy with 5 tap on the desired scene. Once the enroll process is done, you can take UPStart and read an already installed project and then add the phase repeater correctly on free Unit number.
Good success with HLC and also Radio RA2 but Lutron does not support the HLC structure of 32 rooms. You end up with a big bunch of loads that you need to sort in PCAccess advanced programming rooms.
Strangely the fastest reaction time with lighting on Omni is X10 but the reliability on a medium-large scale project is not a good option on top of not having X10 parts anymore like the rs232 two way tx/rx.