Bought this scope about six months ago as I already have the Nikon ED82 which uses most of the same eye pieces. Now I tend to use it more than the larger scope for magnification up to 27x. The twist up eyepiece zoom does go up th 40x but I prefer the wide eyepieces and also the images become less bright at 40x magnification.
The 20x wide eyepiece gives an excellent wide angle view and good brightness and is may favourite. If I had to choose only one eyepiece it would be the 20x wide. The 13-30 zoom with the rubber eye relief is both comfortable and practical to use and very bright at 13x magnification. It performes well up to it's highest magnification of 30x, which is practically the limit of this 50mm scope. Of the two zoom eyepieces available, I much prefer the 13-30x with rubber eye relief to the 13-40x with twist up relief.
When rating this scope I am comparing it to other 50mm scopes in the same league as no 50mm scope will compete on performance at high magnification with a large scope. For a 50mm light weight travel scope, this is the best I have come across and although it works better at lower magnifications, it cannot compete with an ED82mm scope at higher magnifications. The ED50 is quality in a very light weight and small travel sized scope.
Cley Spy and Infocus both make stay on cases for this scope and although not cheap, the Cley Spy cover is of good quality and fits both straight and angled scopes. I have not seen the Infocus cover close up and I believe it only fits the angled scope.