Yes, Yes & Yes
For me anyway.
I changed a few months back from Demon, who seemed to struggle to give me more than 2mbs on a consistent basis.
O2 said they could give me 4.5mbs, so I switched, now pay O2 half what I was paying Demon and get twice the speed (averages 4.8mbs) on a truly unlimited connection. If I had an O2 mobile I've save another fiver, but I'm not switching network just for that.
Customer service is generally quick to answer the phone or email if you need it,and is based in the UK if that matters to you.
Overall, I wish I'd switched ISP earlier, but inertia prevented me acting until my Demon lack of service became untenable...