One advantage of OES is that you get exactly what you want. WB has great products (I own a BMJ), but there are zero options to customize - length, width, cuts, tie-outs, colors, etc, etc. I really like my WB tarp, but I just put in an order for my third OES. I absolutely love the fit/finish Brian puts on his tarps (I also agree with the comments on reflective qualities of grey vs black/dark previously mentioned). To me, they feel handmade from a real craftsman.
I believe Brandon's ridgelines don't need to be sealed, but the side-pulls do. I could be wrong though.
Just my 2-cents