and yes I have used them. The HKS AFR is not as nice or easy to use as the Apex'I unit, but it is also cheaper. HKS does lack however with their turbo timers and such, but they do have a very good niche with ignition and fuel modifying. IE the AFR trims fuel easily, and smooths MAF signal to get rid of momentary rich condition that results from BOVs, just like the AFC. Not everything they offer works well on the Z because of its complex nature, buts lots of their things are very nice.