No experience with the Nippondenso starter.
I did buy an "Arrowhead" starter for my 1150 when I thought I was dealing with a failing starter. These are a Valeo clone and to my great surprise it was actually put together better, the magnet retention in particular being much better than the genuine article.
The thing was however nearly dry so I greased it up before putting it into service, I also went over the a prefer connections as I didn't like the look of one of them.
Lastly I discovered that you can buy a Valeo rebuild kit from a Moto Guzzi dealer for much less than anywhere else. I will put the Valeo back in one day.
As they were only AU$150 I also bought and Arrowhead starter for Airheads. The reason was that I thought the Bosch starter was havi g trouble starting the 860.
However, the fault in both was my own stupid purchase of an inappropriate battery. Lesson learned!