I have always shown mine without glass. I used to be in one of John Stevenson's galleries. He is near the top of galleries showing platinum and at the time I knew him he never used glass. It has a huge impact to walk into a show of photographs with no glass because there are no reflections and they seem much more clear and powerful that way. It is something that doesn't dawn on some viewers, they just notice that photos are really strong and clear.
I showed awhile ago in a place that did framing and they agreed to show without glass however they did a display of one of the platinum prints behind a very expensive non glare glass and it was pretty amazing. I can't afford that type glass but it is almost like glassless.