I went ahead with DITHOR this year for my older who is doing Bigger with Extensions. The DITHOR is totally different, and in my opinion, very necessary. It delves in much deeper to the genres and the comprehension component of literature. It discusses the characters and the Godly traits they do or do not display. It also has you discussing the elements of the story - setting, problem, mood, predicition/inference, cause and effect...and so on. The extension package is only meant to delve deeper into the study of history and historical figures.
Our schedule will be something like this:
~I will read the storytime book aloud per Bigger plans. It tells which Genre and how long to make the book last (i.e. first book is a biography and needs to last 20 days of lessons). All I have to do is take the pg number and divide by 20.
~We will read History/Science togehter and do the activities.
~Then, he will be assigned the History/Science extensions based on the schedule in the back of the the Bigger Manual. Carrie has broken it down into very managable chunks. For instance: Unit 1 he is reading Pedro's Journal for extension. Day 1, he reads pages 1-3, day 2 pages 4-5, day 3 pages 6 and 7, and so on. This is NOT a major reading or time consuming thing!
Finally, he will be doing his reading for DITHOR. You decide which pages he will read and put them on the "Assigned Reading Calendar"...so, again, it is in very managable chunks. He reads what he is assigned to read each day and does the lesson w/mom per the teacher guide instructions. At the end, you do something fun to celebrate the genre and the study you have just done.
So...it really all goes together well, it is all small chunks and managable. The reading is really set and paced by the teacher in DITHOR and with your daily read alouds for story time and the extension package is so small and managable that it is FUN rather than tedious.
Hope this helps!