I have a TalkTalk line as backup the reason is simple the price .
Things you need to know about TalkTalk is telephone support is worthless , when dealing with TalkTalk its best to do it through there members forum .
TalkTalk default profile uses a 12db noise margin , this can be changed by posting a request on the members forum to a 6db noise margin if your line is good enough to support a 6db profile ( most are ).
If not bothered about speed leave on 12db as this will be rock solid unless your line develops a really bad fault and there is a good chance TalkTalk DLM will eventually tune your line to 6db anyway .
In my area i have not experienced congestion for a good few years and a line that was put in as backup and against many peoples opinions ( misconceptions mostly at the time , that unforgivably some still have ) has proved to be reliable and cheap but with shocking telephone support and support is not great in general but manageable through the members forum .
In my experience its been dirt cheap broadband that works , from a budget company with budget support , with most complaints being support related and the telephone support being the biggest culprit .
Other things to remember and this is a big one , is Talktalk take your line away from BT network , this is one of the reasons its so ridiculously cheap but can course problems if wanting to move back to BT network but truth being , if you want to move back to BT , BT retail will take the line back happily whilst signing you into a new contract .