Congratulations for a good start 
My 2 cents on missing features:
- Keyboard shortcuts currently only cover a subset: e.g. going up a folder is customizable but entering a folder is not (e.g. I prefer navigation with left/right arrow keys)
- Quick Filter is my most important productivity feature: instead of only typing some letters of the start of a filename, with Quick Filter you can customize whether it's possible to type letters e.g. from the middle of a filename (useful if many files in a folder have the same prefix like com.apple.). Quick Filter typically also allows to really narrow the file list to the currently matching characters typed.
Have a look at how Total Commander implements this (it really rocks). On Mac currently only Crax implements this (plus the not-Mac-specific cross platform filemanagers like MuCommander and DoubleCommander).

Besides that I +1 the other replies here like customizable editor, sync dirs, compare by content

After a day of full usage I have to say that many features are missing. For Appstore price EUR 1,99, it's good, but if I paid full price, I will be very mad .

- Panels arragement on start it’s 25/75 - Commander don’t remember position.
- Quick Search - don’t search from middle of the file name, it’s not possible to bind quick search to some key (like ALT or SHIFT).
- Possibility to unmount devices from panels, even add context menu.
- Configurable external F4 editor!
- Improve quick look behaviour - it can’t be closed by escape, but inly by key that is binded for.
- Multiple rename!
- Respect localized names of folders.
- Configurable full view columns (remove, add).
- Actual speed of copy/move files/folders.
- Actions indicator in panel icon.
- FTP connection timed out.

What do you think about adding a "Find/Search" function to the built-in viewer?  I find myself opening up text files for quick viewing using F3, but there is no way to search within the file.

Thank you for your feature request. It has been forwarded to our software developers and we will consider  extending standard features of built-in viewer application.

Same behaviour here about panels size. It's 25/75 after start. Version Version 1.0 (1344) - Commander One PRO.

 We assume that you are using the very first version of Commander One, or the edition from App Store, under Mac OS El Capitan. That is why you are experiencing those problems.

If you use version from our web-site, navigate to Commander One main menu --> Check for Updates... and make sure that you are using the latest version. Then, go to Preferences --> Advanced tab, and enable all options, under "Save on quit" list.

In case if you are running App Store edition of Commander One, the only thing we can suggest is waiting till the upgrade with El Capitan compatibility is released.

I've been testing your application and there are some options that I would like to add:

- To decompress a file using another compressor (keka) or to open with ... (application list)

- To decompress files they can be left in the background to perform other tasks

- To have an option to check compressed files

~ I would like to inform you that "Open with" option has been added to Commander One since the latest upgrade of the edition from our web-site.

~ In order to decompress files in the background, open archive in Commander One with double-click, to view its content. Then, drag a file out of the archive or use Copy (F5 def.) option, and queue the copying with F2 key. Here you may find more information about queuing:
http://wiki.eltima.com/user-guides/commander/queue.html

~ We are sorry for possible misudnerstnading, but you can check the compressed files withot a problem. Just open the archive in Commander One to see its content, then choose a file and hit View button (F3 def.), and the file will be decompressed and opened in viewer.   

My 2 cents on missing features:
- Keyboard shortcuts currently only cover a subset: e.g. going up a folder is customizable but entering a folder is not (e.g. I prefer navigation with left/right arrow keys)
- Quick Filter is my most important productivity feature: instead of only typing some letters of the start of a filename, with Quick Filter you can customize whether it's possible to type letters e.g. from the middle of a filename (useful if many files in a folder have the same prefix like com.apple.). Quick Filter typically also allows to really narrow the file list to the currently matching characters typed.
...
Besides that I +1 the other replies here like customizable editor, sync dirs, compare by content

Thank you for your requests, they have been forwarded to our developers along with the others.

First time tried Commander One.

Looks and feels as a very clean and nice application with huge potential! So I'm very much hope you continue the good work.

I'll write down here a few things I'm missing in the application right now, maybe developers will consider them as new features for new releases.
* It seems to be not possible currently to switch between open tabs with keyboard, would be nice to have shortcuts.
* Have a shortcut to open folder in a new tab.
* Have an easy access to the favourite folders list, ideally have a dropbox in the pane similar to the disk dropbox which is accessible with a shortcut.
* As it was mentioned already by others in this thread, configurable Editor is important.
* Same as Editor, would be nice to be able to choose my favourite Terminal application.

Thanks one more time for the good work so far, especially for drive list dropboxes accessible by shortcuts and easy, mouse-free file selection!

* As it was mentioned already by others in this thread, configurable Editor is important.

Being able to choose the editor is a must, it would turn Commander One Pro into the best FTP/SFTP client for Mac OS X –I am an active user of Transmit, Forklift and Yummy FTP Pro and I have good reasons to say so–.

Thanks!
--
Diego