I started using it recently. But, I've made some other tank changes at about the same time. A while back I was using the KZ system and, while it seemed to help, I wasn't sure it was doing anything and it can be fairly expensive, so I stopped. Things when downhill in my tank (although it could have been for other reasons), so, I looked into micro-nutrient dosing again.
I have a mixed reef, with mostly LPS and SPS. I haven't noticed much, if any, difference when dosing trace elements with LPS or mushrooms or even some of the easy SPS (birds nest, montis, etc.). I believe I've seen a significant difference with acropora.
Dosing trace elements very generally is about curing deficiencies. So, unless you have a target level for something, test for it with a reasonably accurate test and identify a deficiency, how do you know what, if anything, you need to add? The simplest answer is that, you don't know for sure. But, that's not the end of the story. I dose quite a bit of two-part in my tank to keep alk/calc stable. The idea behind RedSea Colors is that, while you're not directly testing for trace elements, they are normally consumed at a particular ratio relative to your tank's calc consumption. So, even though you don't necessarily know your trace element levels, you have some sense of their consumption based on calc consumption. This seems like a reasonable approach to me.
Anyway, since starting colors, I've had a few acros that I thought were essentially dead and gone, start to spring back to life. Some others were doing good before and I haven't really noticed any change. I have a couple that weren't doing great before that still appear to not be doing great (I have an aiptasia problem right now and they're stinging/aggravating acros within their reach).
So, ultimately, I think RedSea Colors is generally helping with my acros, not sure about other coral types. I would recommend trying it if you're dosing a lot of alk/calc and not adding trace elements in another way. If you want to be more 'scientific' in your approach, you'll probably need to send some of your water out for trace element testing.
Matt