Is this configuration actually safe out of the box like this? What are the things that I ought to watch out for?
PS: I’ve also read on a post at “the other place” (forgot which thread in particular though) where someone mentioned that it is better if I add a tap between the two terminals at the other end too, thus making it effectively (a pair of (paralleled 18650s) connected in series). Will there be any cons if I do that?
Better keep a soldering iron handy for when that power switch gets a dry joint. It looks rather poorly fixed to the pcb, would be tempted to run some bridgeing wires across the joint if possibly. By out of the box, you mean new yes? not actually taking the thing apart?
I dont know much about series/parallel circuits bit if it was mine i would make sure to fit quality batteries of the same make, capacity and age. Charge them, and check they show the same volts, finally connect the four in parallel for a day to let any slight imbalance even out between the cells, this worked well for me in the past, some sanyo cells i had in series maintained their voltage to a few millivolts of each other throughout the cycle.
So a tap on to the two connections would make it a 2s2p instead of 2s2s as it is now? I dont know, there might be a reason they’ve not done that already, maybe there are wires going under the battery to the control pcb? Srry for rambling on hope that helps.
Thanks for the reply 
I suppose I am just needlessly paranoid. I am still fairly new to these 18650 cells so I have been doing some reading up on their dangers and how to use them safely. But over time I realised that accidents and “incidents” don’t seem to be as common as I thought them to be! Still, it is better to be safe than to be sleeply snugly in a burning house just because I was charging some batteries overnight!