Originally Posted by Daytona

1000000x this. At Shinagawa, you only need to go up one level from the NEX platform to the station level, and the Tokaido Shinkansen transfer gate is like 50 feet away. Compared to Tokyo Station, where you need to go up FIVE levels from the NEX platform to get to the station level. Consider you have first timers and possibly with luggages, it is far easier to transfer at Shinagawa than Tokyo Station.

One additional tip, check the time between when the NEX arrives and when your Shinkansen departs. I do not know when your flight arrives, but for first timers, I would recommend at least 30 minute transfer time so people don't feel rushed and have some time to look at food and drink options or use the restroom if they want to.