Here's why...When you purchase the digital you get access to the teacher's guide and all the student notebooks for that unit. That means that you have total flexibility on where to place your child (you can even bring in additional sheets from the older units). If you have more than 1 or 2 children, you get the most bang for your buck and you have the license to print it as many times as you want within your own immediate family. That means that you can recycle the unit at older levels in a few years and get 2 years of school out of it. Notice how your cost just went exponentially down?
Something to help you price it out is the size. Some units may be a bit bigger or smaller but so far our teachers guide will be about 50 double sided pages (100 printed pages) and the student notebooks are looking to be about 60 double sided pages (120 printed pages). They are all color but most of the student notebooks just have tiny splashes of color to keep them visually appealing but make them easy on your ink tank.
With the print option you will get the printed and spiral bound version of what you need. The benefit to this is that some people don't have quality printers, pay a lot for ink, or just want it done for them and I have you covered!
Please note: If you choose print you will need to purchase the teacher's guide as well as all the student notebooks your children will need.
Bottom line, you have options and don't we all love options?! Both are great choices but depending on your needs and budget, you get to choose the right fit for you!