Yeah the 3 ADSL bonding solution will give you good performance its actually the more common solution. I am one of the few in the Country that got 5 ADSL's bonding. Got a bit over eager I guess.
You going to struggle to find a Linux or open source solution for this to get true channel binding you need special Channel binder on your network and you ISP have to have one
The packets are split apart on your network and brought back together at the ISP's side so you won't be able to get true channel bonding without the ISP playing along
As far as i know Afrihost does not offer this solution you will have to choose between Datapro and TC I'm afraid
There are ADSL joining devices on the market Linksys has them but it is not the same as bonding. With these devices each connection goes down a line so they are not split what I find with this is that one line gets used a lot and the other is idle
It's actually not that hard under Linux. We are doing connection level splitting between two 4 meg lines, and through monitoring we can see that it actually balances very well. It does mean that no single connection will perform better than a 4 meg line. To get full speed you need to run some form of download manager that uses multiple connections. The average web page uses multiple connections to load, and this is where the solution works well. If you need a solid big pipe, then use channel bonding rather. It all depends on what you want to do over those lines.