Using wireless only, in general, devices from one manufacturer will rarely extend the wireless signal of another device from another manufacturer. So, it makes sense to stick with one manufacturer for your routing needs so that you can be assured of compatibility.
Maybe NetComm offers a product to "extend" their devices using wireless only. If not, why not?
As far as we know (and based on our own experience), Linksys will not extend Netgear. D-Link won't extend 2-Wire, etc. There may be some rare exceptions, but I can't think of any, or recall hearing about this on the forum.