As John said, this is not the first pen kit design that uses a "refill extender" piece.
Berea Hardwoods, in their early Sierra click pen kit offering, used a metal extender. . The point of this extender was never very clear to me, other than making the overall length of the pen a little greater. . But it was an inconvenience, especially at the time of refill replacement, because of its potential for getting lost. . As far as I know, there never were any replacement extenders readily available. . And, besides that, who wants to be in the position of owning an unusable pen in the case that the extender disappears. . Some people have claimed (see Curly's post above) that the longer pen barrel was meant to offer the possibility of replacing the standard refill with a gel refill (typically longer) by leaving out the extender piece. . But that possibility was never featured in any of the Berea data on that pen kit, as far as I know. . Similarly, the alternative of using a gel refill is not mentioned in the PSI blurb for this new pen kit offering.
Berea discontinued their Sierra click pen kit with the extender piece about 6 or so years ago when they did a complete redesign. . Some penturners were overjoyed at this change, but many were very confused by the introduction of yet another, different, length of brass tube.
In summary, I am not in favor of a pen which requires a "refill extender", and for that reason I am wary of this new pen kit offering from PSI. . I wish they had provided a longer click mechanism instead of the refill extender.
John, above, says you can eliminate the extender by shortening the brass tube. . I would offer a counter suggestion that the new click mechanism could have been made longer, effectively producing the same end result. . And I would have favored that approach, because I generally do like pens with longer barrels.
Now, having mentioned the new click mechanism in this new PSI pen kit, I am very interested in seeing how this change works out. . This new click mechanism is, as far as I know, a first time introduction in any pen kit that is on the market. . It looks very promising. and it is about time such a new mechanism is introduced. . Now, having said that, there has been a similar-looking click mechanism available for some time (from a couple of sources) for the use of kitless pen makers, so, this new mechanism is not totally new ... just new to the realm of packaged pen kits.