Seems the personal (cost-free) edition now includes all engine features[1], including native plugins. That's changed since 4.6, I think. Though the license mentions some "metrics collection" in the free version, as well as the compulsory splash screen remaining, or at least it did when I looked at the license page[2], which now seems to have AWOLed
[1]http://unity3d.com/unity/engine-features
[2]http://unity3d.com/company/legal/eula