What FTP Download/Upload apps are good on ipad mini?

I am considering an iPad Mini. My job entails me to be available virtually 24/7 to update and fix issues on multiple web sites.

If I am out all day, I don't have the means to do this job. This device seems the most suitable as you can put a nano SIM into it, and use it either on Wi-Fi or pay a small daily fee and use the SIM if wi-fi is unavailable.

The main thing I would be doing, is connecting to a server via an FTP app (any suggestions?), download file(s), editing the scripts, and then uploading to the server.

I'm told that the Apple products are very "locked down", so editing a downloaded file would be very difficult indeed.

I'd like to hear mostly from developers who do similar tasks to this. But anyone who uses the mini would be appreciated as well.

Regards

Simon

UK