Ok, I'll try my best to answer your questions below ....
.... I'm after a piston drive flashlight. Currently have my eyes on the OG of the PD design: McGizmos. However, they are rare and obviously expensive...
The McGizmo PD series were generally produced and released in limited numbers, at the time. I wouldn't consider them "rare" as such, but were never really widely available in the same way that the current Haiku (say) can simply be ordered direct at your convenience.
They have maintained their value well, especially in light of what are now the older emitters they used, but present secondary market pricing is not markedly different compared to back when their small runs were being sold in "waves"
Having done some forum research, there are other options like the Nitecore and Arc6 but generally all PD designs seem to have been discontinued. Are there any PD style flashlights manufactured for sale in 2019? Those that have owned the McGizmos, any comparisons to the cheaper Nitecore or other PD lights?
Any recommendations similar to the OG Ti-PD?
For a variety of reasons, a true piston drive is not the switch of choice for flashlights at this time.
I really am not sure what you are asking about the comparison between McGizmo and Nitecore, but I would say the piston-drive lights of these two makers are about as different as possible from each other, in all but a narrowly-defined technical sense concerning a single part.
Materials, UI, aesthetics, construction, etc, etc, in most every other relevant matter, they differ significantly.
Although neither are common any longer, neither are particularly difficult to try and and find, if you are interested to do so.
The variation(s) which ARE pretty rare / expensive / difficult to find, for completeness, are the @KuKu427 custom titanium runs.
I'm not after big lumens as I already have other lights that serve that purpose. I want to own a PD style light with emphasis on build quality and reliability.
The McGizmo are the most robust of the piston-drive torches, but be aware that the PD design requires more maintenance than most other types of switches.
A rough order of switch durability and reliability, from highest on down, would be ...
• twist ( "battery crusher" type )
• electronic "e-switch"
• piston drive
• mechanical "clicky"
However, in most cases, I would prefer a clicky over a piston-drive for two reasons - ease of (inexpensive) replacement, and less maintenance.
I guess the idea of the piston drive switch seems very unique. Having not had a light with such a switch and reading the rave reviews about the McGizmo pd, I would love to own one. But I guess with the rarity if them; I'm wonder how the other brands might compare?
I am guessing that (as an alternative to the PD) , you may like a flashlight with an e-switch and a ramping UI, such as one of the many Emisar torches.
Hope that all was helpful
