Version 1.8 was released March 21, 2019.
The display of the image is managed completely differently from earlier versions. This makes almost everything much faster and more convenient. In particular, zooming and scrolling are really fast and the overlay is constantly visible. Drawing and erasing are also faster. The only negative is that it usually takes slightly longer to step through the images with the next and prev buttons. On my 2015 iMac it takes less than 1 sec to switch between 50Mpixel images, so this is not too bad. Also, a small border of grey has been added to the image. This helps to make it clear when you are at the edge of the image.
The zoom level is displayed as a percentage, and it is possible to type in a zoom level—click on the displayed zoom level to type in. The zoom level that you step through with ⌘- and ⌘+ have been changed to provide more options and provide overlap with popular applications such as Photoshop, Affinity Photo, Lightroom and Preview (no two of which support a matching set of zoom levels).
Undo/redo of painting and erasing red dots used to be by dot. That could be a slow process, especially now that painting and erasing are much faster. Now the unit of undo/redo is a stroke which is mouse down to mouse up. It is probably best to make multiple short strokes instead of one really long stroke, in order to avoid undoing everything you have drawn at the first small mistake.
There have been ongoing improvements to alignment and composition that have resulted in improved speed and accuracy, especially in dark corners. A side-effect is that the alignment algorithm is less tolerant of camera movement. If you want your images to align accurately make sure that your camera does not move.