I prefer this to Savihost as it is faster and more reliable, it does have it's limitation though, the most apparent it doesn't do VST3, but for just trying out a synth it's good enough. For 32-bit synths I would recommend the Minihost though.
If you're looking for something which can host more than one at a time I recommend the free version of Voltage Modular and use the stand alone as an VST host. Set up a preset with as many VST host modules as you want. It does VST2 and VST3, only 64-bit though.
It is kind of a version of Savihost. A such, it works nearly identical.
Since discussions are disabled on this vst-host, I will put my main critique here:
It forgets its second, third and fourth MIDI Devices from one start to another in the 32-Bit-Incarnation.
With several MIDI Devices, you always have to activate them.
The 64-Bit-Version does not have this problem, but forgets the last path a VST was loaded from, which the 32-Bit-Version doesn't.
Compared to the 32-Bit-Minihost from Tobybear (which is payware, but can be used with a nagscreen without limitations), it doesn't start without a plugin and therefore has no possibility to open a VST from a history (Windows or its own).
For a vst64host it is nice to have it, since several developers are beginning to abandon 32-bit.
But it should be improved for a bit more usability. The aforementioned Minihost has a much bigger feature set.
I use those vsthosts directly on VST dlls to "open with" them, which is the fastest way to test plugins (which don't need installation), and the biggest shortcome of those hosts is that they cannot load a second VST (for example, to test effects), except ashost, which is a bit instable, and Cantabile 2.0 Lite, which is more heavyweight and checks the plugin directory first.
However, since Savihost is already existing and working, I don't quite understand the purpose of Nanohost, except as an advertizing platform for Tone2.