Anyone who ever has had a wall-oven cannot go back to an under-counter oven. Amazingly, many people think that a wall-oven has to be vented. It does not. So, if you have space for a wall-oven you can build one in. And if you have space for a single wall-oven, you have space for a double-wall oven. Or, if you have an under-counter oven, you can add a single wall oven wherever you have space and use the under-counter oven for your second oven.
Here is what a single wall-oven looks like just "placed" on a counter:
Here is what a double wall-oven that fits in a single wall-oven space just "placed" on a counter looks like: