It's a fascinating idea but what worries me is it's Umarex, they don't have a great reputation for standing behind their product. Up to now they have been known for lower quality springers for mass market, and while I applaud their new entry into the entry level PCP market with the Gauntlet, which is a really interesting gun for the price point, the Hammer is WAY out of the lane they are known for. Again, I'll hold off until 1. it actually materializes on the market and 2. it gets wrung out in the field and we get an idea of it's actual durability and how Umarex actually stands behind it if/when problems prop up.
Not an AF cheerleader, I don't own any of their guns, but the SS Texan is a proven design, AF CS is top notch, and 400 FT/LBs with a shroud looks like a lot of win to me. That will probably be my first big bore.