Portscanning the AlphaShield resulted in no response to any probes on the full range of ports from 1 to 65535. I was also able to verify that the Inbound light flashed red instead of green, indicating that it was blocking the unrequested packets from the port scan.
I checked Response (ping) Time and Throughput using Qcheck from the computer connected to the PC port to the machine connected to the Cable/DSL port and measured results of 1ms and 6.7Mbps respectively. So users with typical cable or DSL connections shouldn't see any performance hit due to the AlphaShield's firewalling.
The AlphaShield definitely does provide an effective firewall and, as AlphaShield's product pitch asserts, is certainly more robust than Windows' built-in firewall - SP2 notwithstanding. But although I think it serves its target audience well - the non-technical broadband user with a single computer - I also think that AlphaShield is counting on its target customers' networking naivete a bit too much.
With consumer routers easily available at $50 or less, which include 4 port 10/100 switches, and that provide essentially the same level of protection, I think AlphaShield's $100 pricing is twice what it should be. (Shame on those on-line retailers selling it for as much as $169!) And although AlphaShield's FAQ make it clear that the device does not provide Internet sharing, the FAQ don't make it as clear that using an AlphaShield and a NAT router isn't necessary, or is at least redundant.
That said, the AlphaShield could be the perfect solution for protecting a far-away parent or loved one that is foolish (or uninformed) enough to have their computer tied directly to their broadband modem. And think how proud they'll be when they install it themself!