Yeah, I thought so too, so got GLx 1x and then SLx 3x. Whatever I tried (move the SLx 3x as close as hair width to GLx 1x and then as far as couple of inches between them, as rail allows), the combination doesn't work for me when the magnifier is behind the prism: the sight and mark are all blurry and start to become crisp when eye moves way away from the eye box and at this point magnifier shadow takes over 70% of the picture, so it is not usable. It kind of works when the magnifier is in front of the prism, but picture is still a bit blurry and mark is not crisp too. The eye box is unforgiving and any deviation of an eye from the pair's centerline results in a complete loss of the sight picture.

However, looking through combo (prism in front of the magnifier) with the phone camera reveals that picture is acceptable and mark is visible, which leads me to believe that it's my astigmatism, that makes combo not working for me. This is quite ironic, as I've got GLx 1x prism exactly for this reason: to get clear picture even with astigmatism. It's even more ironic that this same magnifier makes otherwise less than pleasant red/gold dot sight mark pretty nice even without correction lenses and almost flawless with.