I used KBIS for Alice, she was 6 weeks old when they insured her. I just opted for a minimal value (£1000) which is less than it cost for me to breed her, but I was more interested in obtaining full vet care for her.
As she reached one year old she kicked a gate post and needed a fair bit of care. No quibbles and vet paid direct very quickly.
My horses have always been insured by the NFU (30 years) and I was most disappointed at their quote for my homebred. I reluctantly left them but they have priced themselves out of the reach of hobby owners. However for service I would recommend the NFU.