Has anyone ridden the ZipRider in Grindlewald while visiting Switzerland, and if so, what is your opinion of it? Will be there in June 2016 and am considering it for an activity for my teen grandsons.
I haven't been to that particlar attraction but done an almost identical one in Austria. I found it cool but not AMAZING but it was shorter and only had one line. Trying to race each other might add a fun aspect for your boys, but I do not know it they'll synchronize the starts or just send everyone down as soon as the line is clear. Personally I think it's a bit on the pricey side a compared to the one I was at.
I don't know how you picked that one but if you're not tied to Grindelwald there are other such ziplines. Also there are over a dozen high wire parks (Seilpark or Hochseilpark in German) in Switzerland which will often contain some zip lines aside from the parcours.
TL;DR: It is fun. There are alternatives. Only you can figure out if it is fun enough for what it costs...
I would do Fraekmuentegg.
You can start here: http://www.pilatus.ch/
You can do the Lucerne cruise to Alpnachtstad then cogwheel train to top of Mt Pilatus. There are two hotels there at the top and a restaurant or two. And hiking and views. Then a 50 person cable car down to Fraekmuentegg where there are all kinds of things like this. Then a 4 person cable car to Kriens (kree-ENS) and a 15 minute bus ride back to the main Luzern train station--ie the center of the world ;). If you stay stay at Backpackers in Luzern they will give you a big discount on tickets like this that include boats on Lake Luzern.