USB modems are nothing but trouble on Macs, they rely on drivers which rarely get updated by the modem manufacturers, so a future OSX update could easily prevent your Mum getting online if the driver turns out not to be compatible.
Another benefit of choosing a router is that it is inherently more secure because it sits between your computer and the internet. It has a built-in SPI firewall and NAT (network address translation) making it harder for anyone to hack into your computer. If you set the DMZ to point to an unused local IP address, such as 192.168.1.200, your computer will be invisible to the outside world
Yes, the ebuyer router will be fine for any ADSL service.
UKonline LLU

please use you're, your and they're, there, their and to, too and its, it's correctly:
Whilst you're crawling along in your Lada, they're flying there in their Learjet,
proceeding to down too many glasses of champagne from
its galley and commenting "Look down there, it's a skip on wheels". 