They seem really good value compared to other bike specific insurers anyone used them? Any negative or positive stories?

Quote for one bike is still more than my annual home insurance.

Do they require any special security measures which in the real world you are extremely unlikely to follow?

for example carry a 3kg gold standard lock on a 7kg carbon road bike?

Putting bikes under home insurance doesn’t cover them for racing and in most policies doesn’t cover the full value. It requires a gold standard lock for one of my bikes but I don’t tend to leave my bikes when I’m riding them so don’t carry a lock with me anyway.

Doesn’t cover racing I agree, but frankly I’m not bothered by that, even as someone who races quite a bit, but covered for full value and no stipulations whatsoever on locks. Just seems a better solution for me. YMMV.

Putting bikes under home insurance doesn’t cover them for racing and in most policies doesn’t cover the full value

Take out a home insurance that does cover the full value then theres plenty about.

It requires a gold standard lock for one of my bikes but I don’t tend to leave my bikes when I’m riding them so don’t carry a lock with me anyway

So your not covered and paying for something that doesn’t suit your needs.

The only additional cover is sometimes(haven’t checked this policy) bikes left at the transition of a triathlon which is a fairly small market.

Someone pops up weekly asking about these bike specific policies. I imagine at least some have an commercial interest in the business behind the products.
They are imo rather cyclically and dishonestly trying to jump on the cycling bandwagon.

The bottom line though is bike specific insurance would be loss making if it didn’t exclude all the likely risks. Home contents can provide better cover because the combined risk is (including lots of people with no or low value bikes) results in a reasonable loss ratio for the underwriter.