I have the Juki 2010, and use the needle threader all the time. It is quirky for sure! Sometimes I have to try 3 or 4 times to get it to catch the thread. I found, at least for mine, is that I have to hold the thread tight but not too tight - there is a sweet spot that will allow it to catch.
Can't say it doesn't frustrate me though. I have a second machine, the Juki F300, and it's needle threader is much more reliable. It works very differently than the 2010, and I wish the 2010 had it.
However, I do have one of those Dritz needle threader things for backup just in case. I know that so many people have issues I'd rather have some sort of fall back in case mine conks out completely.