Had an opportunity to run side-by-side download tests on ruuter.ee.

I had a Windows Thinkpad with the USB device and a MacBook with the router.

Alternating tests showed the router consistently achieving download speeds of 1000-1500 kbps, while the USB device got 500-800 kbps.
I also tested the USB device on Linux at Võsu yesterday. Download was 60 KBps, Youtube and veoh.com were pretty useable when letting the player to preload a bit, but I think they really need a slightly higher data rate.

I also tried the USB device on the MacBook with PCS Intel modem script. This uses a speed of 930 kbps to talk to the modem. Same results – PPP gets nowhere.