True, in terms of price, duplex is cheaper (though compared to overall router cost that is negligible). In my case, I wanted to be able to swap SFPs if input one dies (for any reason), and it doesn't make a lot of sense to buy different modules for different purposes, even if that would save a bit of money.

There is another difference - if I want to go for field connectors and cut it myself, the Simplex connector would cost about 4.15$, and the Duplex would be 6.16$, which would further increase the price difference.

But thanks for the advice, it is indeed a viable option.