The problem with them is, even if the cutoff points are right for your driver's frequency and phase resonse (which they most likely aren't either), that they are calculated by the manufacturer by assuming the speaker is just a resistive load with the nom. Impedance throughout the whole band. That is not true. A speaker is, when leaving out resonant peaks, behaving more like a resistor (Rdc) and an inductor (Le) in series.
Flip switch to change between assumed load and a more "real world load" and see how it messes up the filter's q factor completely. This does not only sound crappy it can also damage the amp and speaker drivers if you turn it up loud.
