Bit of a black eye for the US in that he trained here, but it's not always possible to predict something like this.
It remains to be seen how he will be put to use. My guess is his main value is recruiting/media. If he turns into another al-Shishani, then it could be more detrimental. I get the feeling that foreign fighters aren't well-integrated or fully trusted, however.
I wonder how many of these guys join groups like IS out of boredom/restlessness rather than fervor. One of my brother-in-law's relatives re-enlisted after a stint in Operation Enduring Freedom because he had trouble adjusting to civilian life.
Similarly, I've think the Chechen wars and the Caucasus Emirate have really been about hatred of Russia rather than jihad. Some of the fighters have said things along the lines of not even knowing how to pray correctly in the Muslim method before getting involved in the fighting.
If they're talking about going door-to-door killing people in their homes, you'd think the US would be towards the bottom of the list of desirable destinations, given our rate of firearm ownership.