Accoding to the FAQs on that linked page it will work for you but as for how secure it will be
If you need internet access, your master computer, in addtion to the USB wireless cards that you are adding, will need a connection to the modem, with that connection being a wired ethernet or USB. However as you would then presumably use Internet Connection Sharing over the USB wireless from the slave to the master, that may proove interesting to setup.
It could well be easier to got the standard method, even if it is a tad more expensive. Get a wireless router and one, not two wireless adaptors. Your main PC can stay wired but now via the router, and you slave gets the wireless.