The ER-6n is the naked version of the Ninja 650R, in fact in Europe it is called the ER-6f (“n” for naked, “f” for faring). Everything is the same, the tune of the engine, the suspension and the steering…it has a slightly tighter rider triangle (your foot peg is closer to your butt) than the Gladius…but other wise, it is very similar…usually in comparison tests the Gladius gets the nod because of the slight edge on Hp (I think it has 5Hp more), and the engine runs slightly smoother (less vibration).
As for the bike being a good beginner, well like the SV650 it is on the edge of what would be recommended for a newbie…but you said that you had ridden before ten years ago, so it shouldn’t be a big deal. The biggest question is what will you be comfortable on, so go and sit on them…a lot…before you make a decission…if you are commuting on the hiway at 60mph most of the time, you may want to consider a bike with some kind of wind protection…the Ninja 650R (obviously), the Yamaha FZ6R, the Honda CBF600 and the Suzuki GSX650F are all in the same ball park…all of these are retuned versions of some potent equipment…they have had new cams and other tweaks to make them more newbie friendly…even they are probably too much bike for the first time rider, but being you are returning to riding, they should be okay.
Anyway, good luck!!