Any review should probably start out with a disclaimer specifying that product review results for something such as a USB peripheral like this cable may vary from hardware set up to set up.
This cable is currently being used with a 2011 15" MBP, 2.2Ghz i7, 8 GB RAM and GarageBand 6.0.2. It was previously used with a 2009 15" MBP 2.4Ghz C2D, 4 GB RAM with virtually the same results. I won't vouch for the performance of this cable on earlier Mac hardware or pre-2010 versions of GarageBand.
First off in regards to the negative reviews: there is no perceptible latency when properly set up.
On the default settings with the original C2D MBP I used this cable with, there was a significant amount. Key word: default. After making the appropriate preference adjustments within GarageBand, there was none.
On the default settings with the i7 MBP, no adjustments needed to be made at all upon launching GarageBand. 100% plug and play. The program automatically recognized the USB link as the default input source and no adjustments were necessary to start recording. The monitor is off by default; clicking it on within GarageBand is the equivalent of flipping the power on a guitar amp if you want to use external speakers, or clicking on the headphone icon if you want to use headphones.
These are issues with GarageBand, not the cable. Any negative reviews based upon lack of basic user knowledge of how to use GarageBand (Apple's software) should be disregarded.
Granted, there was no documentation on how to use Alesis' product with GarageBand (which is Apple's software, not theirs) within the plastic bubble package the product ships in, I didn't personally have to download any of the PDF documentation available on their product support site to make the adjustments and start recording.
In short, with some hardware set ups, this cable may not be one step plug and play simple, but it does work exactly as engineered and without the latency quoted by any negative reviews.
On current Macs with the most recent version of GarageBand and OS updates, it works flawlessly without any set up and is essentially now an idiot-proof product.