I am only using iron:router for my personal side projects. My employer doesn’t use MeteorJS at the moment for any of our client work 
… but that may change in the near future, I am a strong advocate for Meteor internally. For any client work where I would use MeteorJS I would use iron:router if I was using Blaze. I dont see any issues with doing so
Although I believe this router is the only community router being actively developed at the moment that will allow you to use both Blaze or React
I may be wrong about iron:router and whether it is still being actively maintained