The importance of entropy often goes ignored, especially as you look at the cost of devices that provide entropy. A nice alternative to these is the OneRNG, previously on KickStarter and hopefully soon to be available for general purchase.
I currently have the OneRNG connected to a KVM host, however I plan to move it to something else (perhaps a Raspberry Pi 2 or NUC), using Pollen and Pollinate to provide entropy to my internal hosts - perhaps with a few more OneRNGs thrown in for good measure.
You can read more about why entropy is important and how Pollen / Pollinate work here. You can also see the talk given by Jim Cheetham and Paul Campbell at Linux Conf 2015 on the OneRNG below: