After recording a folk group I realised that there were some distinctly dodgy notes on the mandolin, so some of the pitches would need digitally retuning. I downloaded this plugin, and was immediately impressed by the no-nonsense, easy-to-understand gui.
I set the effect to constrain the mandolin part to one key (G major). I set the other controls to minimise the artifacts created by the pitch recognition process. (Obviously, there are always going to be some artifacts of this type.)
For a free VST effect, this really is an astonishing thing, and I am very grateful to the talented developer for making this available.
Even the mandolin player was impressed, and he's a confirmed technophobe !

In choosing marks, it might appear churlish to only give say 8/10 for sound, but to me this indicates that this effect is 8/10ths of the way towards software costing huge amounts of cash. Similarly, I suspect the author is probably worthy of higher than 8/10 for support, but in truth I never needed to call on this service.

I'm rather surprised that I'm the first to review this, but if anybody reading is wondering whether this effect is worth trying, then I say - go ahead, it's excellent !