The slot on the box was very narrow and the paper is flexible, not rigid. I did my best not to look at the ballot, but sometimes I had to look longer because the ballot was hung up.
We asked the regional supervisor three times yesterday for security sleeves and were never given any. I recall about 5 people asking and them accepting my answer.
When I voted in person last time, I argued that I didn't want them to handle my ballot. Finally, they let me put it in the box.
But you're right, not very "secret."