Yes this is very good work. The height maps are indeed excellent. I must have a look at the app you mentioned. I like to use real world height maps too from similar locations. I made some seamless height maps of mountainous areas and then roughly get the height of the map areas desired then multiply the seamless tile by the rough height and it gives the mountains in the places you want it. Its a good way to do it if your tool allows the multiplication of height maps with 16+ bit precision.