Rocketbook vs. Elfinbook: I use both and here is my opinion.
Each of these books has their pros and cons. Hopefully I can outline both for you from my perspective so you can see what you prefer.
Paper: Rocketbook uses a paper that feels more plastic and thin. Elfinbook paper feels more substantial and the ink takes to it much faster. Rocketbook uses a square dot grid pattern, while Elfinbook has lines, much like a normal notebook. So when you scan from Rocketbook, it comes across looking like you just wrote on copy paper (no lines) while Elfinbook comes across with lines for more of that notebook look. For my preference, and others that I've let test, Elfinbook was the clear winner here.
Size: Somewhat arbitrary as I'm guessing both have different sizes. Rocketbook is more of a personal notebook size...think DayTimer size. Elfinbook was larger and a little less convenient to carry around. The drawback with Rocketbook is the size does prohibit the amount of info you can put on a single page. More pages mean more scanning and organizing. Elfinbook held more notes obviously and it is nicer to have more space for sketches, thoughts etc. I call this one a draw, as it is a personal preference. I personally prefer the smaller size.
Page Turning: Odd category I know, but that is why I included it here as I never thought it was a big deal...until now. Hands down, Rockebook wins here with being able to turn the pages just like a spiral bound notebook. Elfinbook, with its thicker pages required me to open the book and fidget with the pages and spine to complete a page turn...without being concerned of ripping near the spine. Rocketbook you can treat like the old school notebooks: flip pages behind current page and keep going. Elfinbook required a lot of effort for me to even want to try and do that.
App Integration: Rocketbook gives you multiple options to instantly send your notes just by simply making the symbol on the page. You've previously told the app where each symbol will send the note. Rocketbook seamlessly reads that and bingo, your document shows up where you told it. Elfinbook is more of a manga process. You have to pick where you want it each time. That becomes a hassle if you use the book for multiple entries (work, personal, diary etc) and have to continually switch where you want it to go. With Rocketbook, I could use 10 pages, each with a different place to go to the cloud just by marking the symbol, take the scan and you are good to go...no delays, no switching after each scan. Rocketbook takes this category.
App: Hands down, Rocketbook's app is more polished. Elfinbook has a ways to go and could be superior with a few updates. Their OCR is horrible (Rocketbook doesn't offer that). Elfinbook has a burst type mode and does seem to capture pages faster with its dark border recognition feature. I give this to Rocketbook again, it is just a more polished app.
All in all, I would take elements of each book to create a better one. I continue to use both, but want my Rocketbook to have lines on the paper, and have the thicker paper from Elfinbook.