I own the GHL. A major advantage was the six puck design, thou the newly available diffuser for the radion greatly helps.
At 12", GHL gives max PAR of 385. The GHL is slightly warmer than Radion (more white LEDs), but you can overdrive the blues. The GHL likely has better spread and uniform distribution compared to a non diffused Radion.
My GHL hits the thermal limit of 65C with fans running at 100%, combined with bluer tint I only get 65-75% of the max 385 PAR. With a Radion, I could probably deliver peak par of 2x.
I love the quality of the light, but today I would go with a diffused Radion because I could get significant more PAR and the software for managing the lights is more 'modern'.
There are probably cases (24-36" wide tank) where you might get away with a single GHL, but you'd need two radions. That can also be a deciding factor.
You need to use the GHL PC software, which can be challenging. You will also have to reset many of the factory defaults (fan speed, thermal limit, etc.). IOW, you will have to ask questions on R2R to get it working the best