And is it just me or the price for leaders carbon track fork ridiculously overpriced?
The Performance fork is a rebranded Kinesis (well, not really, just a different layout on the carbon, it's still branded Kinesis). It's a well built fork, I don't think you should have any issues with it, especially given it's price.
Can I get some confirmation that this would work? Sorry, this is my actual first time buying a zero stack on its own....
This will work.
This headset is an internal headset, which simply means that the bearing cups and bearings that are supplied with the headset will be sitting on the inside of the frame, instead of the outside.
The integrated headset you are getting confused with, is really just bearings, as the cups are already part of the frame's head tube.
So, with some investigation.. The only headset that Leader offers for the 727 and 725, is the FSA ZS3 (carbon spacers) headset. FSA's ZS3 only comes as an internal (thus Zero Stack) headset. So, being said, I think it's a safe bet that you won't be needing any such integrated headset.