What am I missing with this trinket recommendation?

“On use” items set to 1…? Spyglass is ‘On Use’ too, so if you have 1 item max., that’s the better one.

How do I change it so it stays permanently as none?

In the setup step, there is an option called “Max On-Use Items” to adjust how many on-use items you want to allow your solution to have. Set it to No Limit if you don’t want to limit it.