The ERT is a rather fragile piece of equipment that I would not carry in my bag. I am mildly rough with my bag.
I have never had a complaint about a sticker. I have never put one on the hologram either. It actually speeds up the stringing process for me. I try to put the sticker on the butts up side of the racquet throat. When I mount the racquet I can easily see the sticker while stringing. When I am finished I can easily check my last DT number before removing the old sticker. Sure I could open the computer file with this information but I seldom need to.