The ST-63 viewer actually is a much handier viewer than the more commonly seen ST-61 Red-button viewer. It is much smaller and lighter (uses the smaller 'C' batteries instead of 'D' sized batteries in most other viewers). Also one doesn't have to hold a button down, just insert the slide! Although it's a real tight fit, I've been able to fit a halogen lamp into the one pictured above (for extra bright white light).

On the down side, it has no interoccular adjustment, only a focus adjustment (the red dial). Which means if one likes it, it's no big deal, but if one doesn't, then that's about it for the unit.

The other downside is only a possible one. Some of the units have single-element lenses while others have the better dual-element achromat type of lens (which all red-button ST-61's have). The one above has the good lenses (easy to tell using a slide with sharp white black edges -- it'll show rainbows on the edges with the non-achromat version of lenses).

I've found that the ST-63 seems to go for less than half of the price of a red-button ST-61, but can be about as good to use if the interoccular is okay with the user (which it should for most people) and if it has the achromat lenses.

One weakness than I've seen in a number of units is that the green plastic has a crack going from the red focus wheel to the front (near your nose when using it). This can make it difficult to "hold together" (top doesn't want to stay on). It probably can be repaired although I haven't tried to fix one as yet.