I have vals, riccia and java mosses (regular and peacock) in my tanks. I dose Excel everyday. They have not shown any damage. I think the problem comes when people use the overdosing method to combat algae.
I also think these plants get use to being exposed to this. I think when you have sensitive plants it is best not to use the large dose prescribed for after large water changes. Start with the lower daily dosing and let these plants get use to this.