I had 12 prints mounted on Dibond by Digital Silver Imaging (high end printer/framer in Belmont, MA). I love the finished product (no reflections in dark areas from glass, no huge cost for museum glass.) They suggested protective spray for durability and resistance to fingerprints, sneezes, etc. And since they are a Hahnemuhle Certified Studio, they use the Hahnemuhle protective spray. As my prints were on Epson Exhibition Fiber, which is soft, I opted for the spray and am happy with it.
Of course untested mixes of products (Epson paper with Hahnemulhle spray) produces an end result of unknown archival properties, but my feeling is that these two manufacturers are serious and the combination is likely to last for a very long time. I would be interested to hear the opinions of others on this. But the refections from glass have always bothered me, and even more so with the capabilities of Piezigraphy!