Though the Altima chip gives the VPN1 10/100 auto MDI / MDI-X Ethernet capability, performance is limited by the USB interface on the other side of the device. My quick tests with IXIA's Chariot showed performance less than the blazing fast results I got in my SX41 performance tests, which I attribute to the VPN1's USB side.
Maximum non-tunnel throughput averaged about 5.8Mbps, with little variation during my one minute Chariot run. Running the same test through the IPsec tunnel yielded a 1.5Mbps throughput - fast enough to keep up with most cable modem and residential broadband connections.
It's pretty frustrating to pay only about $60 for a VPN endpoint router and then have to cough up at least twice that to buy an IPsec software client. Although it is possible to get WinXP's IPsec client to work with the SX41, the USBVPN1 is a much easier-to-use solution for connection to either the SX41 or its more powerful sibling, the BEFVP41.
Even though its limited configuration options won't work with all IPsec gateways, and it won't do you a bit of good if your on-the-road connection is via a wireless hotspot, the VPN1 should provide an easy-to-use and reasonably-priced alternative for basic IPsec VPN connection.