I started using nutricote or dynamite sustained release pellets a few years ago as I was bad about fertilizing the Cyms - always just watered with the hose.
My two small flowered Cyms have always bloomed well with just the sustained release fertilizer, but the larger flowered ones less so - tho they are also older and had at times been subjected to extended periods of neglect...
Like I said, the Cym next to this one, which has bloomed nicely (smaller blooms) - 2-3 nice spikes every year for the few years I've had it - has really busted out with spikes and buds this year after changing to less sustained release fert and adding some water soluble - 8 spikes, over 200 buds!
So, for myself at least, I will continue with using both - maybe bumping up th water soluble a bit.