I did buy some of the Red River San Gabriel. I don't care for it and won't buy it again. In my mind, it continues the Red River theme of lower cost materials, but at the cost of clearly lower quality goods. To be fair, it is cheaper than Canson Baryta Photographique, but not enough to justify my using it.
It's a 300 weight material, but feels lighter and flimsier than the weight number would predict. The surface is light pebbled, which I don't mind, but the sheets emerge from my 4900 with faint surface scratches (in the direction of the paper path) that annoy, and which I do not see on Canson Platine and Baryta (my go-to's). The RR canned profile seems quite inaccurate for soft-proofing, as it predicts a very, very warm and saturated image on my system. The paper reacts to reds, on my system, in a funny way in that they are disproportionately represented. By this I mean a facial portrait with rosy cheeks looks mildly clownish. Again, to be fair, I'm sure a well made custom profile would level that out. The white point of the paper is in line with the Canson Baryta white point, which is decent considering the RR's non-OBA claim.
I could see San Gabriel being useful for a project when saving 15% on media costs really makes a difference. That doesn't describe my world, so I'll recuse myself from opining further, as I guess I'm not the target audience for the product.
John Caldwell