I have purchased Nock Co's Maryapple as part of their initial Kickstarter campagin back in Oct 2013. I didn't get a chance to use the Maryapple at all because I was working on a Muji A5 hard cover notebook then. However, that's all changed now that I am done with that notebook.
What is a Maryapple you ask? It is Nock Co's two memo book bi fold holder. It fits memo book with dimensions of 3.5" x 5.5". It handmade in USA with durable materials. 1000D nylon with DWR coating on the exterior and nylon pack cloth on the interior. The stitching is tight and ample. I have confidence that it wouldn't fray easily.
Maryapple comes with two pockets. You don't have to keep only 2 notebooks inside the pockets. As far as I can pack it in, each pocket can hold 3 Field Notes memo books in each pocket comfortably. However, you don't have to limit yourself to only memo books. You can clip your pens in the pocket if you do not mind your pens touching. Some may prefer a leather memo book holder but Maryapple is lighter and it comes in quite a few colour ways.
In conclusion, I highly recommend the Maryapple to all who uses memo books. I am sure that it will be able to withstand all the rigours of being carried around all day. Pair this with Nock Co's Lookout and they will be the perfect EDC carry. Click here to read a review of the Lookout.