I got my Indivision AGA MK3 last week, and I really like it. However, there is one missing feature that really makes it harder to work with the MK3 than I think it needs to be.
That feature is the ability use a regular Amiga resolution such as PAL or NTSC with the native or common resolutions of today's widescreen monitors, for example 1920x1080 without the image looking stretched.
Currently, the MK3 will always fill the selected monitor resolution with the selected part of the Amiga resolution. For PAL, that means a resolution of 640x512 will be stretched to fit in 1920x1080. However, that doesn't look right because the Amiga uses a (roughly) 4:3 aspect ratio and the monitor a 16:9 aspect ratio.
My feature request is to add a setting that makes sure that the image is scaled to the same degree in the X and Y directions. So with 640x512 -> 1920x1080, that means the Amiga's 512 lines are scaled by a factor 2.11 to fit the 1080 lines of the monitor, and then the horizontal scaling is also a factor 2.11 so 1350. That means 1920 - 1350 = 570 pixels per line aren't used, so 285 pixel wide black bars are added to the left and the right of the Amiga's picture.
(Of course the black bars could also be above and below the Amiga's image, for instance NTSC 640x400 on 1280x1024 would be 1280x800 + 112 line black bars above and below.)
It would be even better to fill the bars with the Amiga's border color or perhaps a user-definable color, but letterboxing/pillarboxing is normally done with black bars so black only is totally fine.