I have the physical one, but much prefer to bring a PDF with me out of house. These days I put everything wargaming on my Remarkable, and it helps keep the actual books in good condition (dragging a heavy paperback everywhere is murder on the poor thing).
I can. It is a bit pricey perhaps, but I got it through work and it completely changed the way I make lists (I am back to writing them by hand) and bring rules along to games (all PDFs).