Gfilui

I am using now the HxD editor (which is a windows program, with wine).

I also have tried some GUI based (I am not interested in CLI) hex editors for linux.

Some criteria which is important for my preferences:

• 
  

  When the opened file is changed, it should automatically reload.

  
  
  
  • In bless e.g. you must click the reload button.
  
  
  • In HxD it reload by itself (even when used as a wine program on linux).
  
  


• 
  

  To change the amount of bytes in a row easily.

  
  
  
  • In bless you literally change the width of the window to change the amount of bytes per row.
  
  
  • In wxHexEditor e.g. you must go Options -> Preferences and then change the number
  
  
  • In HxD you change it directly in the tool bar
  
  


• 
  

  It should be very easy to modify on the fly some bytes in hex.

  
  
  

  • In wxHexEditor to change some bytes it feels something awkeward.

  
  

  • In bless you do by default inserting new bytes (but I do not need insert too much, more changing bytes)

  
  

  • In HxD it is working (for me) very fluently.

  
  

There are some more criteria too, but these three are for me the most important ones. (also only tried out bless and wxHexEditor)

For me it does not matter what program or plugin for a program is used to fulfill my basic criteria but most important thing is: it should be (if possible) a linux program (also open source, or free to use).

Otherwise I will still use HxD (even if it is a windows program, I do not care, it should work and fulfill my preferences).

Update

For trying out, if the program is fulling correctly the reload preference, you can simply use this little python program:
Simple numpy IO file program

Also this programs I will not use unless they can be changed to be optimized for my use:

bless, wxHexEditor, GHex

You might look at GHex. I don't know if it'll meet your specs, but I think it's worth a look.

In terminal...

sudo apt-get update

sudo apt-get install ghex

Or you can probably find it in the Software app.