The NBG318S and PLA450 will each set you back around $100, so this isn't an inexpensive way to improve your wireless coverage. But it was able to provide around 14 Mbps of throughput in my home's Wi-Fi dead zones, which is better than any other products that I've tried.
That being said, if you want to try this method, you might be better off using your current router and buying a pair of HomePlug AV adapters and a cheap 11g router to turn into an extension AP, particularly if you're a gamer and/or heavy Torrent downloader. With the going rate for HomePlug AV adapters running around $70 each, you won't save much over using Zyxel's solution. But you'll probably be happier with your current router's routing performance than you will with the NBG318S'.
One other caveat before you take the HomePlug plunge. All alternative (to Ethernet) networking technologies have their weaknesses and HomePlug is no exception. Where 2.4 GHz Wi-Fi performance suffers from neighboring networks, cordless phones, microwaves and more, HomePlug performance is sensitive to power line noise.
In particular, fluorescent lights and light dimmers can really knock down HomePlug throughput. And you really have to follow the installation instructions regarding plugging HomePlug adapters directly into the wall, especially avoiding power strips with line filtering and surge protection.
So the answer to the question posed at the top of the review is no, HomePlug AV + 802.11g does not equal Wi-Fi Nirvana. But it can provide another, although expensive, way to provide a 10-15 Mbps network connection to places where CAT 5e can't go.