I have one of these. It's a common reference book for the Antiochians (others may use it, I just don't know). I bought it about a year ago, though I don't remember from which bookseller. I seem to remember that I paid about $25 for it. It's chunky in shape, so looks heavier than it actually is - nowhere near five pounds, though like you that is exactly what I've heard it called. My little mission parish has very little in the way of liturgical resources. This is a fairly efficient way of checking for many items, though it is far from complete and not always user-friendly. But I have learned to find my way around it reasonably well. There are occasional explanations for why and how some things are done that I find useful as I have no formal training. I'm a layman leading the chanting in our services, so I do a fair amount of helping our priest organize our services. I'll check resources I've collected from here and there over the last few years and make suggestions to our priest for what we (the chanters) might be able to do, and verify that services are put together as properly as we can with available resources. Of course, my priest has the final say in all these matters.
So, anyway, I find the book useful in my situation, though I'm looking forward to the time when the parish can afford to purchase more complete books.