Copy protection third-party toolkits

I need to add copy protection by license to a desktop Qt application that runs on Windows and OS X. We are mostly interested in per-machine licensing, with the possibility to issue time-based trial licenses. At least initially, a simple manual off-line license validation (we can just email the activation key to the user) will just do. Possibility to go for on-line validation will be considered later on down the line.

I see there are many third-party toolkits available, with seemingly analogous features, capabilities and pricing. Does anyone have some specific experience on the matter, and can provide recommendation on a particular product?

Thanks.

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