The obvious difference is that the Redmonts is mined while the Celtic salt is actually naturally sundried Sea Water. The CSS is light grey and a little moist. The both claim to have lots of trace minerals. It would be interesting to do a side by side comarison from an actual chemical analisys.
There's a testimonial in the front page of the RS site from someone comparing it to Celtic Sea Salt and saying that the Real Salt tasted much better. It could just be a matter of subjective personal taste but it makes me curious enough to wanna try is and compare it to the Celtic stuff. I have a Whole Foods 1 blk from my house and another great healthfood store within 3 or 4 blks so I'll prolly pick up some of the Real Salt and do a side by side taste test in the next day or 2 and report my test here.