Would anyone be able to share what's the difference between buying the same policies (eg health) from different insurers and what's the USP of each companies that make you choose one over the other?

Product features are generally the same across the different insurers though there may be some minor differences.

What's mainly different will be from actuarial (pricing) and underwriting standpoints. The latter will depend on how strictly the underwriters follow their reinsurer underwriting guidelines and whether they have the capacity to override. This means that some insurers may offer applicants with medical conditions on standard while others may choose to impose loading / exclusion or decline the risk.

So if you happen to have a preexisting medical condition, best to use preliminary underwriting first before submitting formal paperwork. This is to prevent you from having to declare adverse underwriting decisions in future applications.

Different premiums and coverage