If you've got the bits, good to use them It seems that it was well worth it too, as some background came to me also:
The Sunder keep many of their traditions and procedures from their days as loyalists, in some ways even more so as traitors. As a brother would once aspire to join the Kindred as the pinnacle of martial art, so he does as a Chaos Marine. Joining such an exalted cadre is surely the best way to acquire more glory, and find more to devote themselves to for Slaanesh? The progression of a Marine darkly mirrors that of a loyalist chapter, even down to such veterans leading their newer brothers in battle. What better way to strengthen the Sunder, and therefore lead to great glory in the future? Of course, it is conveniently a great way to steal more glory for yourself...
As the nascent Chaos band formed under the Kindred's auspices they slowly acquired new members as those beneath them proved themselves before veteran eyes, and those of their new patron. The Kindred's famous (soon to be infamous) Tartaros armour could not supply them all, but thanks to being free of the leash of the Codex Astartes small bands of power armoured Kindred formed and started gaining their own glory.
In time the Sunder settled into their new form, and their way of devoting themselves to their god. This lead to an offshoot of those Kindred most devoted to Slaanesh, but no less in their skill and bonds of brotherhood. Taking on golden masks, all blessed under a Dark Crozius, they formed dark pacts and called themselves "the faith takers". In battle they are utterly silent, even their bolters and chainswords eerily so - at least until they bite into flesh. Yet they burst into maniacal laughter with apparently randomness in the midst of battle, and it is claimed this is the moment that their opponent's resolve is broken - their faith taken to be fed to Slaanesh.