Need help with Sequential Shifter

[Kuma]

Ok, as the title says, my question is about sequential shifters.

When you use a sequential shifter, do you need to have a sequential gearbox?
The product I wanted to know about is this:
Sequential Shifter

Thanks!

[spinnanz]

They convert your H pattern to sequential. They are also a waste of time and are said to be hard on the box.