I have a Wavetrac, very happy with it. Extremely smooth, practically imperceptible in it's engagement. No drama of fuss, it just gets the job done. Eliminates torque steer too.
I expect others are good, but I can only speak for Wavetrac, they're are also using unique patented technologies, see here:
http://www.wavetrac.net/technical.htmThey're beautifully made, here's mine going in at JKM. My Mk5 is 2009 so was just on the handover to Mk6. It turned out that I have Mk6 transmission which was a surprise.
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There is no doubt though that any LSD is a massive improvement over an open diff. As previously mentioned, buy from one of the bigger names in the business and you won't fail to be impressed.