On ISO compatibility:
There are many options to give ISO compatibilty to an ANSI US set. The XT layout is the easiest and cheapest one. It only requires four keys on top of the ANSI US layout:
Item | Profile | Legend | Size |
1 | C-D | Enter | ISO |
2 | C | `~ | 1 |
3 | B | \| | 1 |
4 | B | Shift | 1.25 |
This layout is not new, nor something just made up, it was extensively used in the eighties in keyboards for most XT IBM compatible computers. It allows the use of an ISO Enter in ANSI US layouts with no redundant legends. This is a very effective and cost efficient way to offer basic ISO compatibility to an ANSI US based set.
The second less demanding ISO compatibility option for an US set is implementing an UK layout. This requires five extra keys, over the XT layout:
Item | Profile | Legend | Size |
1 | E | ` ¬ | 1 |
2 | E | 2 " | 1 |
3 | E | 3 £ | 1 |
4 | C | ' @ | 1 |
5 | C | # ~ | 1 |
Any other ISO based Language requires many more extra keys. This may be better acomplished with an International set.
The two ISO alpha keys that you included in this base set, along with the ISO modifiers, belong to the German ISO layout. They have redundant legends with the US standard. The XT keys that I suggest may be a better fit for that small ISO compatibility pack. The German ISO requires more than twenty extra keys, so including a couple of them does not accomplish it. I really do not understand why some recent GMK sets have included them. They may only serve as placeholders.
An example of the XT layout.