VMware vFlash and Hybrid storage

[Valdereth]

So I'm going through the VCP550D exam blueprint (anyone else out there taking this before the end of the month?) and I reallized one of the VMware features I have little experience with is vSphere Flash Read Cache, or vFlash.  I'm curious if anyone has done any testing or worked with this, especially with an environment powered by a hybrid or flash equipped array like Nimble.  How much benefit does vFlash offer in an environment powered by a Nimble array, if any?  On paper, I can see how it might offer some complimentary options, but real world might work out to be much different.

Anyone care to weigh in?