When you enter an nsec into nostr:npub1v5ufyh4lkeslgxxcclg8f0hzazhaw7rsrhvfquxzm2fk64c72hps45n0v5 or nostr:npub1getal6ykt05fsz5nqu4uld09nfj3y3qxmv8crys4aeut53unfvlqr80nfm or nostr:npub1tnpfz60snm7ler8k8c69335n37we6690qttl88t556yzkjxhahjq3kkkpe extension, do they see it or not? 
Where is it stored?
Why do people say it isn’t a good idea to enter one’s nsec into many apps?