Cons and pros in single cell and series configuration?
Im mostly thinking about safety..
Even for plain ICR cells, the abuse they're able to survive is pretty dramatic. This from the ICR18650-28A datasheet:
9. Safety
9.1 Overcharge Test
Test method: To charge the standard charged cell with 12V and 2.8A at 25℃
for 2.5 hours.
Criteria: No fire, and no explosion.
9.2 External Short-circuit Test
Test method: To short-circuit the standard charged cell by connecting positive and
negative terminal by less than 50mΩ wire for 3hours.
Criteria: No fire, and no explosion.
9.3 Reverse Charge Test
Test method: To charge the standard charged cell with charge current 2.8A
By –12V for 2.5 hours.
Criteria: No fire, and no explosion.
9.4 Heating Test
Test method: To heat up the standard charged cell at heating rate 5℃ per minute up to
130℃ and keep the cell in oven for 60 minutes.
Criteria: No fire, and no explosion.
This is valid for UL approved cells, but not for cheap Chinese cells.
Its safest not to own any lights which require a series configuration at all.
Next would be quality protected cells.
Then generic protected cells.
Then IMR cells.
Then unprotected ICR cells.
Then protected whateverFire cells.
Then unprotected crapFire cells.
Next step would be to put blackpowder in the flashlight and place it on the oven.
Single cell lights:
same order as above, except for the first point.
What do unprotected laptop pulls fall under?
I took a look at my ultrafire “protected” cells I got back when I knew nothing about liion… there isn’t even a protection circuit on them… 
Blackpowder is also probably safer than unprotected xxxxFire. 
Laptop pulls = ICR if it's a good brand like LG, Samsung, Sony, Panasonic, Sanyo..
I trust quality (Japanese?) unprotected cells more than protected cells, many of which have had the protection circuit slapped on by a third party. The last batch of protected cells I bought arrived with one of the protection circuits DOA. But then, I keep a close eye on cell voltage and seldom let them get below 3.6v in either case.
I think the protection circuitry on chinese cells is often of poor quality, but it may not matter. If the cells are used in a high current application you probably need to remove the protection to get the max current available.
I wouldn’t go with unprotected cells.
RMM’s protected panasonics seem to have nice high quality protection.
Evva vs. Keeppower NCR18650B Protection PCB Visual Comparison
Quality Seiko protection IC & 3 good MOSFETs. Same as keeppower except keeppower only has 2 of those MOSFETs.
Seen a couple teardowns of clear wrapped panasonics or other cells with protection added by mystery companies. There is no quality chip like seiko. Instead they tend to use a chip by a Taiwanese company, fortune semiconductor, chip marked DW01.
I think protected cells were a temporary answer to early problems, and that in general the protection is going to go into the main circuit and not the cells. I am a 1x user in both AA and AAA, so I am thinking no real need for me to buy protected, plus so far the protected cells I’ve bought are slightly longer causing some issues in some devices.