I see really no excuse for not providing pressure relief. Granted they typically don't provide much protection against violent cell ruptures but they do protect against a slow leaking cell and pressure buildup. Can be either a lip "o-ring" seal or just a switch boot bulging out. The important thing is to prevent such pressure that the metal container strip the threads which can be quite violent.
Low LiIon voltage protection - that's the battery's job. A low voltage warning is optional and really just more of a convenience than a safety feature. There's really no excuse for not using protected LiIon cells since they're much too dangerous to be used unprotected - LiFePO4 is the exception; You just ruin the cell. Like can't absorb overcharge, dangerous to charge if cell voltage is below a certain point etc. Right, some says that protection circuits are not 100% safe either. Well can't argue about that. But lets says it's 99,999% safe (99,999% chance it's diong what it's designed to). Then you can use it with dirt cheap chargers and if you use it with good quality charger that's lets say 99,9% safe (I'd bet chargers in general are much more unsafe than the protection circuits due to complexity). Combined then you end up with 99.999999 % safety on the electronics side. Of course in the calculation there's not the factor of the cells themselves. Like some manufacturers recently had grains of metallic lithium in their cells leading them to random thermal runaway even with no abuse. But I believe you get the idea why a protected LiIons is a really great idea.
