Yes, it's fibre optic. Switching depends on the extra you might get vs the cost. For me it was a no-brainer because I live so far from the exchange I used to get 150Kb on ADSL but with infinity I get 30Mb so a twenty fold increase. It's reliable and means much less waiting for things to download.
Amazon Fire HD 8 review: A brilliant combination of function and value – with one massive caveat