Rosewill, through its tie-up with ATNG, has managed to offer a very good PSU with great efficiency, tight voltage regulation, and, on top of these, silent operation. In general, the Fortress 550W left me very satisfied and I think that it justifies, at least to some extent, its high price with the performance it achieves and with its 7-year warranty.
Nevertheless, I noticed some issues that need improvements such as having only two PCIe connectors which limits the PSU's usability and restricts its usage to mainstream-medium systems. In my opinion, this unit could easily handle an additional pair of PCIe connectors which would make it much more attractive to potential buyers.
Also, because of my bias for high-end platforms, I would like to see a little lower ripple on all rails. It doesn't mean, however, that the ripple of the Fortress 550W will cause any issues.

To sum up, this product is somewhat pricey considering that it is just a 550W PSU with native cables only, but it does have other things to offer such as its exceptional performance, quiet operation, and a lengthy 7 year warranty. So if you don't mind the lack of modular cables and you don't need more than two PCIe connectors, this great-performing PSU is worth the buy.