Never been displeased with my parasite engine, and the one time I coupled Parasite & Pain (I'm still new to DE, only a few games under my belt) it worked marvelously. Cronos opened up, killed a termie, gave the talos a pain token. Talos opened up (TL-LG, TL-SC) on the same termie squad (5 termies, their shoulder-missile launcher thing, assault cannon), charged, survived overwatch unscathed due to FNP, and ate termies for breakfast.
My only question for you is this; why are you using 15pts to get the additional CCW if the only upgrade you're taking is chain-flails? In my experience, TL-LG for 10 pts less > +1 attack for an extra 10 points every time.
I dedicate these deaths to Odin Allfather, Spearshaker, One Eye.
Fleet Shadowmaker - Kabal of the Dying Sun; Cult of Marrow Excised; Coven of Lambent Hunger
Sons of the Last Breath - Chaos Space Marines
Host of Shattered Purity - Chaos Daemons