Hello untelepathic,
In our onspeed page there is an explanation of how onspeed works:
When your web browser requests a web page the Onspeed software redirects that request to the Onspeed compression servers. They take the web page content, compress it and send it back down to the Onspeed software which decompresses it and sends it to the browser requesting the information. In this way Onspeed can significantly increase the speed of web surfing and email downloads.
From my personal experience it works wonders with Dial-up connection. It makes web surfing almost as responsive as broadband. This is why I recommend onspeed for dial-up users in areas where ADSL is not available.
In the case of broadband onspeed can help only in the downloads of large uncompressed websites where the compression done by onspeed will be a benefit greater than the added latency. The fastest your broadband is, the fewer the cases onspeed can make a difference.
Onspeed offers a 14-day money back guarantee which you can use, and probably you should unless onspeed is installed on a computer which could be used with a dial-up or GPRS connection in the near future.