We use SL but I don't know too much about OM. So-
Choppiness- I think this is more a problem with the early Cores. I am going to do P 4/5 with my 4 y.o. this fall but we will just read through the books without the guide. It sounds like the guide breaks up the books into ridiculously small portions. Core A might be like this too, I don't know. I have used Core B, C, and D and don't find them to be at all choppy.
There is a lot of reading, compared to some other curriculums. But I don't think it is more reading than if we were doing exactly what TWTM recommends. Even doing 2 Cores, it has been very manageable, though my three that have been doing it are older, so they have been reading more independently.
We have the wiggles too. Some of the read-aloud assignments are long. I let the kids do Legos, blocks, color, etc. as long as they can tell me what we read about at the end.