The current login model is only really simple if a user is comfortable sharing their app permissions to Google. If not, it's tedious at best.
1) Recommend have a simple password login option like many other apps.
2) New invitees receive a Code, not a link, and it can only be used directly in the form LK takes you to after you enter your email address. If you close the browser because the email took a long time to send, you have to start over. Poor user experience.
3) The email takes a long time to arrive (seems to be on average > 3 minutes) and the code says it expires in 10 minutes.