I live in Finland where I write in Swedish and Finnish and have to be able to easily type åäö/ÅÄÖ. Appart from typing these characters I prefer the US keyboard layout over the Finnish/Swedish keyboard layout, as the keys on the US keyboard are better placed for programming (which I do). I only have my keyboard connected to Windows computers, but very much use Linux through SSH (and Cygwin and Windows Subsystem for Linux).
On the Model 01, I used the normal US keyboard layout as a base and placed åäö on the function layer where these characters would be on a normal Finnish/Swedish keyboard, i.e. on the =’; keys on the US keyboard (right of P and L). I programmed these keys (on the function layer) to send the key codes International 1, International 2 and International 3 respectively.
I then made a new keyboard layout for Windows using KbdEdit (http://www.kbdedit.com/, I have a license for KbdEdit Premium), where I used the standard US keyboard keymap as a base and added mappings from Int 1, 2, 3 to åäö.
In addition to the åäö characters I have added a dead key for acute and grave accent on the function layer of the backtick ` key (right of Q), mainly so I can type é which is sometimes needed in Swedish. This key sends “Non-US \ and |” a.k.a. Europe 2.
On computers where I don’t have my custom keymap on I can use the standard US keymap, but will not be able to type åäö.
I could use a standard Finnish keymap in Windows (or any other OS) and do more customizations on the Model 01 so that I could maintain the general US keyboard layout and also be able to type åäö. One reason that I am not doing that, is that the way I am doing it now also works with my Truly Ergonomic Keyboards (TEK) that I have been using for three years. These keyboards do not allow as flexible programming as the Model 01 — you can only change what key codes it sends — and the way I’m doing it was the only solution. Another reason is that I have noticed that some applications in Windows (e.g. Adobe Photoshop) don’t respect the keymap but instead use the key codes directly, and assume the keys are where they would be on US keyboard.
On my TEK I have the åäö chars placed under more convient fingers instead of the right pinky that I have on the Model 01. I decided to place them where I have them now, so that they have to same location as on a standard Finnish/Swedish keyboard for muscle memory reasons. Also, I now have the more convient places for other, more frequently used chars.