The early (1st release) version of their retracts, with the nylon cap ends were junk.

The upgraded ones are a lot more solid , but I have heard reports that the odd pair leak badly, though this may be because of faults in the air connectors.

If you visit the KMP Website, you can find pics of the upgraded units and compare them with the ones in the kit to see which version the kit your looking at, comes with.

Those that have decided to "junk" the supplied units (usually 1st version) and given feedback on this forum seem to favour either Century Jet or Robarts retracts. Opinion of which is best, seems to be divided.

I can give no opinion on the retracts you mention.