I have a Rock BR, which is a significant upgrade over the Rock Deluxe or Jr. After owning all 3 of these listed, the BR version is the only one I can say is worth owning, and even then, it's not a rest I would recommend. I can say the Rock tests are better than a sandbag or bipod, but barely so. The bald eagle and Sinclair varmint rests are a much better value. The Bald Eagle is probably the best value in a budget front rest, coming in under $200 regularly, and often around $175.
The downside to the Rock is the slop in the elevation threads. It just induces too much movement. Even with the BR version, the elevation slop is too much to really allow use of the windage head, and the BR has far less slop in the head elevator than the lesser models.