I recently received and assembled a Nixie Clock Kit (not my kit) for my birthday. However, there's a 180V no-touch area. With 2 kids, I wanted to build in a little extra safety to keep fingers from wandering into the danger zone. It also helps to block out stray light since I use it as a bedside clock. If you use ABS and polish it, it also reflects a little bit of light inside the clock that gives it a cool effect. Black works well, but I bet a translucent (t-glase or similar) filament would look pretty good too.
If you do pick up one of those kits, be sure to get the acrylic frame for it as well as this frame relies on it to stay in place.