I have ridden one and it was a lot of fun. Although not even close to the WR250X I had at the time which was much more practical for me: nice open seating position, nearly the same power, two sets of wheels (street and dirt), excellent suspension.
Downside: it's high. And expensive. I paid about the same as for a new Ninja 300, but the WR was a year old and had 700 miles on it.
From my perspective the Ninja 300 is a great back road screamer, lots of fun with the light weight and an engine you can rev and wring. But I wouldn't want to do any touring on it. The leg position for me is super uncomfortable (34" inseam), lean forward isn't too bad, still too much plastic for a beginner bike in my opinion, but okay, if it's cheap enough.
I'd always prefer a 500 to 600cc twin over a 250cc for anything that has to do with more relaxed riding or anything that includes longer distance. Not that it can't be done of course, I just plain wouldn't want to. It comes down that not everything that's possible is also a good idea.
Sure, everybody is different, so the Ninjette might be a good option, if you fit, and if it fits your riding profile and what you expect from a bike.
I would just not try to argue for one with power-to-weight ratio or sport touring comfort ...