One aspect to take into account is that there has been numerous past reviews and comments about the various 20x80's - most of them measure in the 18x71/72 mm size.
The 15x70's from Garrett / Oberwerk et. al. measure close to there stated size. These 15x70 versions get primarily excellent reviews and comments on C.N's.
They give a 66 degree Afov. They display very good light transmission and give a bright / contrasty image.
They have very robust build qualities.
There Q. and A. is excellent.
I use my 15x70's over my 20x80 triplets about 80% of the time as the image is so appealing.

Good luck
Chris