Dyna CDI ignitions - any good?

I found the following CDI ignition on ebay and it claims up to 9 horsepower increase, which isn't a lot for $550
Would you need an exhaust, airbox and possibly flatsides to those gains, but if you had exhaust, airbox, flatsides would you need this? And where would I put it?
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380066544773&sspagename=STRK%3AMEWAX%3AIT&viewitem=

Would you need an exhaust, airbox and possibly flatsides to those gains, but if you had exhaust, airbox, flatsides would you need this? And where would I put it?
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380066544773&sspagename=STRK%3AMEWAX%3AIT&viewitem=