I think it very much depends on where you come from and what kind of subscriptions you have access to in your country. I travel relatively often for work and worldwide 3G or LTE is much more important for me than dual-sim.

I don't mind dual-sim at all, it can be useful to some and is inexpensive, so why not. I'm actually happy I have it on the Jolla C even though I don't need it personally, it helped me convincing my girlfriend that it was a good phone for her since she's a foreigner and did not want to give up her phone number when she moved in another country.

But in my own case, there is just no need for another SIM. I am currently an expat for two years and did not even consider changing my subscription for a local one, the subscription I have in my home country gives me unlimited international calls/texts/mms and 50 GB of fair use wherever I want (16€/month), so it works during short trips as well. Worldwide data network is by far what matters the most for me.