I have been using TC's 2-channel bonding service for good while (since the product's early days).
So far so good.
However, the data quality of one's ADSL lines will still be a contributing factor to the available download speed (even at 4Mbps/line).
Our box is close to the relevant ADSL exchange... so the service performs relatively well (Telkom ADSL permitting, of course).
As an aside: there is a significant technical difference between bonding and balancing of multiple lines.
Balancing is easy to do. There are at least a dozen over-the-counter modems/routers that will do this.
The primary benefit of a bonding solution is a single static external IP address. Bonding is not nearly as simple to accomplish as balancing (specifically in the South African context). Bonding normally requires the consent of the ADSL physical layer provider (i.e. Telkom). Telkom does not consent to ISP's bonding lines together (to do so, would threaten its very lucrative Diginet service). As a result, Technology Concepts uses a far more sophisticated bonding technique than would normally be required in a deregulated environment.
I am not aware of any service available in South Africa (other than Technology Concepts) that does offer an ADSL bonding service.
I know that IS does offer a static IP solution, but that isn't on 4Mbps lines that are bonded into a single address.
