I was on a jury duty mailing list a few years ago. At the time I worked offshore, the letters always arrived a week before mobilising. I eventually found out I could get a 5 year opt-out if I went to the local court office in Dingwall and signed some forms and took proof of employment. It wasn't that I didn't want to do it as a "duty", but as one of only 2 people on the rotation for my vessel, the upheaval would have been significant, and my employer didn't have to pay me for that time either. And yes -you only get what you said in compensation, actually from memory you can claim travel also, but only by the cheapest form of public transport (bit like signing on). So if you take a train at say £5, when the bus costs £3 they'll only compensate you for the bus IF you have the tickets.
My father did it years ago, at least if I remember correctly, he went to court about 6 times but sat on a bench outside, never even got inside the courtroom. He was retired, but even that was a faff.
Luckily I haven't been sent any letters since. Just as well because I'm self employed now and have to travel outside the UK for work and the loss of earnings would be enormous. Good luck with it, even if you do get called to the court building I don't think there's even a guarantee you'll get inside the actual door when you get there. It all seems a bit fickled, like tax returns, once they've got your name, you're on their radar for a long time.
Rich