I'll chime in here on the other side.
The tranny in the PF (and I think it's twin in the El Grande BP) is my favorite of any made.
For me, the way the transmission extends/locks the refill in place with an almost audible "snick" (my word [
)] ) is very satisfying. On the issue of the way the top of the tranny engages the inner locking tube, I measure before I finish turning. Sometimes I shorten the upper tube some to make sure the tranny fully and completely engages the inner tube. I'm probably overly cautious on this issue because many of the PF's I make are recessed clip with a closed end on the top so I have to make sure my length is correct long before I get to actually assemble the pen.
So let's talk about what we're comparing it to.
Standard 7mm: yes, it's steel, but in my experience suffers from far more slippage in the tube than does the PF tranny. Also, I have never quite been able to get over the sluggish feel of the 7mm trannys. Yes, for the most part they twist out and lock in place just fine, but the feel just doesn't grab me the way the PF does. Grab what is considered to be a high end BP, (come on , I know you've all got a Mont Blanc sitting around somewhere. [}
] ) Twist it to extend out the tip. How does it feel. More like a 7mm or more like a PF?
Double twist (cigar, etc): I HATE these. To me, these just scream cheap! You always wonder if you're really in that "center" spot where the refill is up. Twist it too hard the wrong way and you are unscrewing the whole pen.
I really like the PF and would highly recommend it to anyone. True it's not the simplest kit to make and make well, but the finished product IMONSHO can be one of the best you can make in a BP.