I first used one of these tests after a friend of mine complained that she'd changed her provider to get a faster connection, but then found it was actually slower than before.
The test I did showed that my connection was also a lot slower than my provider had promised, but after a phone call and an online diagnostics test, they managed to speed things up a bit.
If you are paying for a high-speed DSL connection it's worth checking that you're actually getting what you're paying for.
