As your Nuki Keyturner is installed on the insided of your door, nobody will recognise that you have Nuki in use. Thus, burglars can’t gain any advantage and there is no impact on your insurance coverage. Nuki has no impact on the security class of your door and your insurance coverage. It is not necessary to inform your insurance company about it.
If you lose your mechanical key, you have to exchange your cylinder. But when you use Nuki, you just need to withdraw the access permission of your lost smartphone and generate a new permission for the new smartphone.