I recently spotted a thread over on the AVS Forums comparing the Zyxel NSA 325 and the Netgear ReadyNAS Duo v2.
I'll admit that Zyxel is one company I don't have a lot of experience with. A fair number of the reviews I've seen have indicated that the Zyxel unit might not have quite the same feature list or polish that ReadyNAS provides, but the Zyxel NSA325 is often available for a slightly lower price than the more expensive ReadyNAS Duo v2.
Sometimes it's easy just to go with what you're used to, and that certainly can be an obvious reason to stick with the ReadyNAS if you're used to Netgear products. There can be a tangible benefit to knowing the software you'll be working with. Still, if you're looking for a discount NAS and aren't necessarily concerned that it is the most polished product on the market, it might be worth considering making the switch to Zyxel's model.