Hello There
I have the 18mm, 15mm, and 12mm. There was a test study that found that the 15mm was the best of the bunch. That is according to a reply I read at stargazerslounge.com. I would have to agree with that test study. The 15mm is my favorite. All three are way better than stock eyepieces that come with a new scope. I have read that below 12mm the eye relief is kinda tight. In fact the 15mm has better eye relief than the 12mm. The 25mm is a dud. Opinions vary. Here is a link
https://stargazerslounge.com/topic/3...ers-supertest/
My three main scopes are all F8. Focal ratio is a major factor in eyepiece performance.