They give great power increases, especially with the complete manifold and system.
They are pretty loud-boomy, Ashley deal with the budget end of the market their build quality isnt briliant but a lot better than sportex. they also take a little jiggleing to fit. This was my experience of them on a mk1 astra. I took it off because it was too boomy but that was pesonal taste. They make them for budget competition use where long life isnt that important but cheap power gains are.