ross980
In answer to your questions
What are the other advantages? Fun and see others below
They look like they’d be really hard work to pedal, are they? no, if they don’t make you fitter they will kill you
Are they good on boggy moorland stuff? Yes, unless it’s very, very boggy
Can you climb steeper stuff due to extra grip? Yes if you run low pressures
Do the tyres act a bit like suspension, Yes, but with loads of rebound
or do you have to run them rock hard so they don’t drag too much. – No not at all any more than 10 PSI is too high, unless your road riding, but if you are road riding Fat Bikes aren’t for you.
Get a test ride on one, I’ve got 2 (and a half fat)