Changing email clients is a major chore, and I suspect that there's a good chance I might return to my boring old mail client after the initial delight of the new client wears off... With those odds, paying $10 for software that I probably won't end up using is not appealing.

Also, I feel that the word "beautiful" should be banished from app marketing copy. There are many things in this world that are beautiful, but I hope my threshold for beauty never gets so low that a grid view of email attachments would qualify -- that sounds like a state of mental disorder, experiencing Stendhal syndrome when faced with a GUI.