I was with NFU for many years and they were always good to deal with. However this year I have cancelled my insurance (I have separate 3rd party liability cover) as my horses are now 17+ and the premium rocketed up this year. I have put £5,000 into a separate account and am adding the equivalent of my monthly premiums into it to cover vet fees.
I'm also with NFU, I'd had my boy for approx 3 months before we started having medical issues - he ended up going for a full workup and diagnosed with PSD, had the surgery, did the rehab. Paid up no problem at all. He then went lame in the front after the surgery and rehab and went back again for another workup, including MRIs and remedial shoeing - again paid up with no issues. Very impressed. My insurance premium went up £200 between renewals and like eggs debating not renewing in November as the conditions will be excluded and it may be more prudent to have an emergency fund for vet bills where he is concerned! But would 100% recommend - I have phoned them a lot with lots of noob questions over the last year (first horse, never had to deal with insurance before) and everyone I spoke to was kind, explained how it all works, no question was too silly for them.
I'm another one who used NFU and found them to be excellent in all respects. Old Horse is now 29, and semi-retired. Not insured as we only bimble about on our own land (with the necessary violent spooks and leaps at nothing much . . .) and any injury/colic etc would result in immediate euthanasia.