My sericol RFU neons showed up and I just ran some tests. First impression: WOW!
The attached image shows the following from top to bottom:
1. Brightest I could get with Matsui Glow Green pigment and brite base.
2. Sericol Flu Green out of the can with 6% activator
3. 50% Sericol Flu Green / 50% Sericol Flu Yellow out of the can with 6% activator
4. 33% Sericol Flu Green / 67% Sericol Flu Yellow out of the can with 6% activator
5. Sericol Flu Yellow out of the can with 6% activator
All swatches printed on Anvil 980 Heather Dark Gray (60% poly/40% cotton)
In person I think the 50/50 looks both the brightest and the most like a classic 80s neon green. 3 and 4 both almost hurt your eyes to look at. They smell...interesting...when curing. Nothing like Matsui, but still not "good". Great consistency out of the can and i have had an uncured bit of ink sitting out for about 25 minutes and it isn't noticeably drying.
edit: messed with the white balance a bit on my phone's camera. In real life the matsui and the flu yellow look closer to the second photo, but the other three look more like the first photo.