the Livewire is better than the Xcal 2 no doubt. you can datalog for long periods of time without a computer and you can set it to warn you if some parameters aren't being met, like going lean. on top of that, you've got the cool features of a shift light, digital gauges, and the hp/tq estimaters. the a/f ratio readings will be as accurate as the wideband setup you use is. as long as you have a properly calibrated wideband, the Livewire will be 100% accurate.