You will notice that the light have lost a ton of output when the battery starts to get close to 3V. And once its that low, you get lots of "extended runtime" due to the low output on high. The more I have tested low voltage limits, the less afraid I am om running my batteries low. Because output goes down a lot in a single cell light (atleast when you expect high to have 1000-1500++ lumen) And with a Qlite, you always have that safety, which always have worked when I have tested it.
Ive got no worries running unprotected cells in a setup like this. With the stock driver, that would be a different story. I just feel much safer having a cut off. Its is a great safety feature if your light for some reason should accidentally be turned on due to getting the switch pressed in. If there is a short circuit inside a light, you just fry a spring. So driver circuits can prevent undervoltage. Springs can prevent insane battery drain/short circuits. And if you use a good charger that will not overcharge, there is not much to worry about. Especially not if you monitor your cells.
When that is said. If not having a cut-off Im using protected cells in most lights. My previous mod features a custom "R86" version of the Drjones lumodrv. Its got low voltage cut off among other changes. (I have not tested yet though, partially because a Drjones drivers have a feature to extent runtime by a lot below 3V. Takes ages to drain a cell :p )
Anyway, just test it yourself and get acquainted with how the output drops.
There are some small voltmeters on ebay and various places that can be nice to bring "out in the field" in order to check battery voltage..