Oops, late to the party. Here is my best answer...
I have nothing against loops, they are better than the naked eye and definitely better than assuming what your edge is like.
I use scopes exclusively. They don't only show you EVERYTHING but they also help you improve on your mistakes and create your own progressions, remember this is an art. Creating and edge is like drawing a picture, no 2 are the same.
"shave test is the ultimate test"
This is something I hear almost every day, however I don't fully agree although it does tell you a lot. The shave test doesn't tell you if your edge is pitted, foiled, burred, nor does it show you a false edge or wire edge if it has developed. Both tests are important.
Here is an example..
For demo purposes I have created micro chips on an edge on one of my razors and have taken a photo using both a jewelers loop and a microscope and I think we have a clear winner. I'll let you be your own judge.
Here is the photo that I've just taken of what I'd call a "bad edge" with my jewelers loop, looks fantastic here! (it's a cheap ebay loop which says 40x but I don't believe so)
Here is the same razor in the same spot taken by my 400x microscope, The toothiness is much clearer through this magnification, it will still shave well but the edge may not hold up very long and the edge will feel aggressive.
Which one do you get?
If you don't take honing too seriously and just want to do edges for yourself then you can survive with a loop.
If you are a honing nerd, perfectionist, willing to improve day by day and have a "sharp fetish". Or if you're doing edges for others apart from yourself well you know the answer.
Have fun!
