CLZ is fantastic, and to me it's worth every penny. I order new books online, but I also like to go into my local shop. While in the shop, I find it very useful to be able to pull up what I already have on order, so that I don't re-buy it.
I find it reassuring also that the developers are very active, continually making new features and enhancing the product. If you're using Excel or something like that, you'll be thrilled with it. With so many volumes of different books these days and their respective variants, being able to see pictures of all the covers is very helpful, enabling you to quickly pick and include a book into your collection. I have rarely encountered books that weren't easy to find in the database, and when it's occurred, inputting the bar code number has brought it up immediately.
I have multiple collections in mine e.g. "Ungraded", "Graded" and I have an "On Order" one which is helpful, so when they arrive I just add them to one of the other collections.
Just use the free trial and put in a bunch of books and see if you like it.