I use both in my mix of things (I also use freeze dried pods and rotifiers with them). The Brightwell RB XC seems to not raise PO4 as much, which is good in some of my tanks, but bad in others. Whole other story there, but a few tanks I have a PO4 limited. But I do seem to get a good response from my LPS and zoas with it.
If you experience higher PO4, you could try it in place of the reef roids every other feeding and it should help to reduce PO4 a little.
For saying if it actually makes things grow, I cannot say. Like I said, I see a response and things do eat it and things do grow. How much it helps them., I have no idea. I just enjoy wathing the feeder tents grab it up and slurp it down lol.