Former Link user here.
As far as the manual says, the G4 extreme used to be exactly the same as the current V88. Most likely the current G4 extreme had its features removed so people would have a reason to buy the Vipec over the Link.
The hardware is mostly the same. They have the same boards, just with different outputs on each. The processor is exactly the same.
I haven't tried the Vipec software, but I would wager that it would also be pretty much a copy of the Link software, with the logos replaced with Vipec ones.
In your situation, the added features of the Vipec (current controlled injector drivers, electronic TB control) are useless, so it would be waste to buy one... unless for some retarded reason you plan to use those features in the future.
I personally prefer the Link because they have more information available on their website. Although I'm sure 98% of it would apply to both anyway.