TeX Writer - LaTeX On The Go 4+

I use this app a lot to write notes and tutorials for my courses and it has been an invaluable tool for me. For anybody with memories of old implementations of LaTeX on Mac OS (for example OzTeX), the way this app. automatically fetches packages online when needed simply seems magical.
The one main weakness for me was the shaky DropBox support. Yes, it worked, but only as long as the DropBox folder was only used to push edits done on the iOS side. Any work done on the macOS side would invariably lead to conflicts that this App was doing a terrible job of solving (pretty much, the only solution was to flush the entire folder). Fortunately, v. 4 seems to have solved virtually all DropBox problems for me. It really works the way it should. Many thanks to the developer.
The only remaining minor irritants are that the editor is limited. Yes I know that I can modify the config file to change the presets, but it is somewhat cumbersome. I used to hate the copying mechanism that the developer seems to be very proud of... I just got used to it and it doesn't bother me as much as it used to.
Anyway, this is one of a handful of apps that are absolutely essential on my iPad and that I use every day. I Love it!

I use LaTeX on my computer, and it's so convenient to have it on my iPad and iPhone 6 Plus as well. It makes me so productive since I can work and make documents anywhere and any time. I love how it integrates with other apps. I use a combined file browser, file server, FTP client app, Documents, and I can move my Tex and PDF files back and forth between the apps.
The new text editor is much better than the original and a lot easier to use.
The one thing I think would be helpful is have a video tutorial to show us how the app works and explain how to use the features.
The app developer is responsive and fixes issues with the app quickly, so if you have problems, don't hesitate to email. I've had some problems before, and they have all been fixed around a week after I reported them.

[Written a few months before Version 5: Although some automatic sync isn’t great, it has much better version control. Incredibly stable and easy to use a wide-variety of packages (I was particularly impressed with how easy it was to make advanced geometric figures with tikz). Very happy I purchased it.]

I just recently updated to the Version 5. This was a massive improvement. The automatic sync is still wanting (as in, I need to hit “sync” whenever I think about it in order to sync my documents), but the editor is fantastic. Split view has made this a supremely useable and productive editor for myself. I still prefer TeXStudio on my computer, but on the go this is the best option.