I have personal experience assembling 5 of the Jaycar WideBand O2 kits. Nicely packaged and went together well. just make sure that you are good at soldering and have the proper power supply to calibrate the kit after it's assembled.
These kit's look to me like they are just a specialized voltmeter, measuring the voltage coming from the Oxygen Sensor. You can just use a voltmeter to read the voltage from the sensor to ground, and get the same information. 0.5 volt's is what the ecu shoot's for, but I generally see it go between 0.3 and 0.8, which is about 12:1, up to about 18:1.
I didn't see any wide band kit listed on their site. Additionally a wideband sensor generally run's between $180 and $360, by itself.
Thanks, I got the digital A/F meter, the high range temp switch with LCD, and the Dalek voice kit. Seeing the A/F ratio will give me more car-oh-feedback so I can prove/disprove the Hot Air Intake for myself. I like the high temp switch because I can use it in lots of different ways:
1 - Create a switch for HAI temp control.
2 - Before / After engine block temp readings to see if the HAI is putting my engine at risk.
3 - Creating an alarm for my wife's pottery kiln.