Only problem with using a piggy back fuel controller is the Altezza runs a closed loop ECU. The ECU will eventually over ride any adjustment to the air/fuel ratio you make. You can get around this by resetting the ECU every couple of months (bit of a hassle really). The proper way around this is to go the whole hog & get an APEXi Power FC or Greddy E-Manage.
When I first purchased my Altezza I looked at the Camcon-T
. I'd had an APEXi SAFCII in my previous car (Levin BZ-G) & was happy with the gains it gave me. I asked a few guys on the ACOA/NZ forums about them & thats when I found out about the closed loop ecu's & subsequent problems. Have a read here of what I found http://z4.invisionfree.com/lexusaltezza ... topic=6867
Would be cheaper just to reinstall your factory air box & get a APEXi or K&N panel filter IMO.
All I can say is if you do decide to go down the SAFCII/Neo route make sure you get it professionally tuned on a dyno.