A "courtesy car" from a generalist insurer is usually a base-spec petrol hatchback with private (social, domestic, pleasure + commuting) insurance only. Drive for Uber in it and you're uninsured. TfL can suspend your plate. The insurer can void the policy.
Specialist accident management firms (us, and a small number of competitors) maintain fleets specifically licensed for hire-and-reward use, with full TfL Private Hire Vehicle (PHV) compliance. That's what "like-for-like" actually means in this market.
Why category matters: if you normally take Uber Comfort or Bolt Comfort bookings in a 2020+ Prius and we put you in a base 2014 Auris, you drop to Uber Standard / Bolt Premium. Your hourly earnings fall ~25%. We track which Uber tiers each fleet vehicle qualifies for so we can place the right swap, not just any swap.