We use React Router on our project. Looks like 4.0 does break pretty much everything.

My thoughts on the upgrade are pretty much:

- Do we actually need to upgrade? Old react router works fine.

- If we do need to upgrade - how long will it take? If it's just a few hours to shift some code around, maybe it's not that bad. Especially if it's moving to a cleaner more "react" API.

At the end of the day, we could write our own routing class, or another. We'll probably stick with react-router though - but save the upgrade for a day where we've got nothing else to do, or if an engineer has some free time.