Yes you are correct with that. I think Bryan maybe failed to add that he uses a Reeflink or it's hooked up to a controller like the Apex.
I would personally steer away from the AI Prime. Not that it's bad, however I just feel you may regret the decision when your corals really fill in.
From personal experience, I find the AI Hydra is much easier programmed than the Radion. I usually would get frustrated when I would program my Radions. When it came to the Hydras, it was extremely user friendly and easy to program.
Both are outstanding lights though and will grow whatever wherever. You will not go wrong with either light. Though if you're considering the XR15 vs Hydra 26, you're not going to really have a major difference in pricing. The only difference will be controllability. Like I mentioned, the AI comes WIFI ready right out of the box without spending an extra $100 on a controller. That's just my big thing. So yes, you can absolutely control your AI Hydra HD's with your phone/computer right out of the box. All you have to do is connect your phone to your AI Hydra HD, connect it to your wireless network, and it's ready to go.
In fact, I was going to go with the Radion XR30 Pro Gen. 4 on my Reefer 170. But I just couldn't justify the $900 price tag for the Light + Mount opposed to $350 for the Hydra.