I'm only speculating here too, but my thoughts are the Vamo already has short circuit protection built in and If you are using verified IMR batteries And you have the correct sized spring preferably a Hot Spring you really don't need a ShortStop or a VapeSafe 2c. The correct spring will cost you +$2.50~ and no further issues or a ShortStop that might cause the Vamo to not work at optimum level for $15.
I understand how these come in handy when using mechanical mods especially so when stacking batteries but I also understand that when using VV's the danger only appears if the short happens whilst the batteries have just been installed fully charged (no drop off) are totally unprotected (not IMR) or with batteries that do not use safe chemistry Then you would be wise to use a ShortStop or VapeSafe or similar, otherwise it's superfluous to requirement. Yes? No?
Is it necessary? Absolutely not. Is it superfluous? I don't believe so.
My thinking is this: IF you have to modify it in some fashion to snug up the 18650 battery, why not use an inexpensive add on that provides an extra layer of protection? Granted, the device itself has built in protections, but electronics can and do fail. A ShortStop or VapeSafe as a spacer that also provides additional protection seems like a logical solution for those that care to implement it. If Vamo users would rather stretch the spring, replace the spring, or use a magnet spacer, that's their choice. I was just sharing an alternative solution.