It's more like - what do you value more: usefulness or looks. Gremlins have their own very high physics impact damage(30). Vipers have... well, the only practical difference from Afuris is grineer-tech high crit chance. They are cool to shoot fast, but... I can't think how to use a weapon that shoots for one second and reloads for two seconds. Seriously. Perhaps you need to get it reload mod(Stunning Speed) and at least Ice Storm(clip size), but even then it only makes you burn through ammo. So it looks cool, it can do decent burst in terms of DPS, but other than that - it's useless. It may be a direct upgrade of Afuris(much like Gremlins own Akbolto), but it still has nothing to compensate it's terrible ammo management. Long reload, small clip, weak damage... If it had innate ammo mutation(like pickups would give 50% more ammo), along with better clip and bigger base ammo(like Grakata) - sure, it could be taken as equal weapon to Gremlins in terms of sustained dps. But in it's current state... you dump Gunslinger+Lethal Torrent to Gremlins - you get Gremvipers. You dump Gunslinger+LT on Vipes - you get 60% of shots missed, clip burned in half a second. Figure.
Gremlins, the ammo efficiency on the Vipers is terrible, and they don't pierce armor. And this from a guy who loves the Twin Vipers. They look, sound, and feel cool, but they're practically useless past low levels.