Protected Lithium-Ion and IMR batteries (more about Li-Ion and IMR batteries in another post) have a small electronic circuit integrated into the cell packaging. This circuit protects the battery against common dangers, such as overcharge, over discharge, short circuit/over current, and temperature. Protected batteries are safer to use in your light especially if the person using the cells does not understand the safe handling of Li-Ion/IMR cells. Protected batteries are less likely to ignite and cause personal or property damage due to the added protection circuit.
Modlite supplies protected cells in all the complete lights it sells. We feel that protected cells are generally the safest to use. This will get some push back from the battery geek squad but as a manufacturer we need to design to the lowest common denominator, so the extra safety of protected cells is what we offer and recommend. We do however sell unprotected cells and some of these cells offer a bit more current that protected cells due to the protection circuit limiter.
That said with proper handling and storage of cells and with the use of quality chargers such as the Nitecore chargers use of non-protected cells is very safe. So ultimately what cell you choose is up to you. We do recommend that whatever cell you use can deliver at least 8amps of current and be purchased from a quality vendor and not Amazon or eBay which is known for selling re-packaged cells which at a minimum can be of poor quality or at the extreme explode during use or charging.