The stock haldex has stock mode. The modified controller is the same thing, but it just allows you to adjust the built in safety net in the haldex system.
Do a hard pull off, do your front wheels spin but the backs standing still and you bog? Well, you putting too much torque through the system and it's cutting it down.. I think the limit is set at 350Nm or thereabouts, if you're chipped you pushing more than that through it. The adjustable controller allows you to push more through the system, but at the same time is putting a lot of extra strain on the system. It's a good thing you are buying it with the cable switch, leaving it in sport is really not recommended for day to day driving.
If anyone has any more up to date info on this then please feel free to correct me, but I've spend a lot of time talking to the people who actually made this and finding out about it, but it has been a while and I might have misremebered one or two things.. They couldnt guarantee that it will improve 1/4 times or the like, it should as it does allow you to pull off more aggressively but really it wasnt made for that and more for track racing.
Looking forward to your reviews of it in SA conditions, but apparantly there is a car or two in Durban that is already running this but not on any of the forums.