I have been playing venoms my last games 4 or 5 of them and obviously Flayed Skull. They aren't competitive, but i think that they are a playable option. In a list with ravagers and talos, venoms go unnoticed the first turns, and the lvl of the scenery are very important too of their survible, but their are to weak for their cost.
If I had to sugest some change, their should be the range of the splinter cannon from 36" to 48". With a rapid fire distance of 24" you don't need move the venom in front to the mouth of the rival units to shot but you're close enough to be objective of their bolter or equivalent weapon, and even units on foot could take the splinter cannon like a viable option.