I'm currently using an Iroscope, however also have Zeiss, Leica, Scienscope, Kyowa and optika available. The Leica is very special indeed and gives beautifully clear images. The Zeiss is also good. If the rest, even the worst is more than ok for my poor eyes to perform the finest of SMD soldering.
I know I would struggle with a non zoom scope, and a 0.5x barlow lens is essential to provide adequate working distance. Things like 0603 resistors I'm soldering with minimal magnification, perhaps only 5x, however if I want a close look at a fine pitched IC then I want at least 20x magnification.