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I don't personally have one, but I've used one and I have to say it seemed to be fine, this obviously depends on which area you are currently using it in. Costs depend on how much data per month your provider offers, as of now in Italy you can find plans that go for €13/month which offer 50 GBs/month and unlimited traffic in night time (0:00-8:00).
I went to S.Korea last month and whilst on holiday I rented a mobile hotspot from the airport.
Maybe it's because UK mobile networks aren't that great but whist there I was surprised by how good the reception and internet speeds were. (I get around 40Mbps ish) For 4 days it costed around £22