Blinking effects are very powerful, especially when you are allowed to abuse enter the battlefield effects such as Derevi, Empyrial Tactician, Karmic Guide, and dozens of others. He’s a solid card that for only 5 mana is a 4/4 vigilant trampler which is pretty relevant. Having a blink ability on him as well is great.
While not a Commander that I'd choose to run myself, he’s a very good option. Roon can become quite a Voltron general if you can load him up with enough Auras and/or equipment. That trample and vigilance truly makes a difference when he goes to beat players down!
All in all, Roon is a great creature for any Bant-themed (green/white/blue) Commander deck. He can be a very strong Commander to build around in a variety of ways and can be a useful contributor to most decks that can abuse enter the battlefield abilities. He's certainly one of the better Commander exclusive Legendary Creatures.