Protected battery - is it still necessary for these SFs?

When I started out with Pila LiIons decade and a half ago, I was made to understand that using protective circuit on mod'd light was the best way to go. Also got to do with the Pila charger which had no detection on voltage readings.

LiIon technology and chemistry had advanced thru the years. Is it still necessary to use protection circuit on most lights?

I acquired a couple of Surefires and had them bored for 18650 :
- U2 with emitter mod'd with XP-L HI.
- stock P2x Fury.

I would like to use unprotected 18650s on them, essentially due to their lesser diameter over those with protection circuit-added.

I'm currently experimenting a Samsung 30Q (button top), but had to removed the add-on (thick) transparent wrap.

You can always use unprotected batteries.
It is primarily recommended for beginners to use only protected batteries. At the general danger situation with the use of LiIo batteries, however, hardly changed anything.
With 15 years of experience, you now know for sure where the danger points lie, for example, Overcharge, deep discharge, short circuit, polarity reversal, etc., which protect the protection circuit.
If you use unprotected, you should definitely pay more attention.

I'm now running unprotected Sanyo-Panny 18650's in two of my ZL's. No problem or issue at all. In my dual battery light, I run protected Orbtronics. I try to keep it very simple after all these years.

There's pros/cons with anything in life. Generally, for cells in series (positive end to negative end) protection circuits (PCBs) are still a prudent choice because cells can become dissimilar and eventually lead to reverse charging.

For single cell lights, PCBs were prudent back in the earlier days when the lithium-cobalt chemistry (ICR) was more prevalent, as it had a lower thermal runaway point than the two other common chemistries--lithium-manganese (IMR) and lithium-ferrite (IFR).

Nowadays, with hybrid chemistries and their higher TRPs, it's less of a concern in single cell lights.

PCBs can fail, but they do offer beginners some peace-of-mind, notwithstanding.

I don't personally use them as a rule, but do own some.

Chris