This Bushnell erect image porro prism yields images that are both upright and laterally correct, and does so with straight-through viewing.  Occasionally a telescope with straight viewing is preferrable to 45° or 90° viewing, but with straight viewing you lose some brightness versus a 45° or 90° angle.  Nonetheless many users keep such a device handy, especially for terrestrial applications where the scope is nearly level to the ground.