I hope you'll like it. I've put quite some effort in making it useful, that is I've thought through which use cases there are and designed the app to be able to answer those questions.
For example if you have a high precision distance scale, you often just want to set the near and far limits and get the answer to which focus distance and f-stop to set, while if you have a live view you focus at some object at some specific distance and then want to know which f-stop to use to cover a specific range.
The tilt screen is a bit more complex, but one can start simple with that. If you have live view you really don't need to calculate the focus distance, you just focus at the middle of the tallest feature in the scene. You then only use the calculator to calculate which tilt to set to get a specific hinge distance, and then the span to figure out which f-stop is required to cover the tallest object in the scene. If you have a high precision focusing ring you can calculate exactly which focus distance to set too.
The "virtual ground" feature of the tilt screen is intended for the use case where you put the hinge distance a fair bit below the ground to gain wedge span. This is useful for longer lenses, say 70mm and up when it comes to medium format. You can then see when the DoF wedge comes up through the ground and make sure that it's before the ground becomes visible within the field of view.
I use the app myself with Linhof Techno and ground glass focusing, and a rangefinder for checking distances. I don't always use the rangefinder though, in general the distances you're interested in are fairly close and after a while one gets quite good at estimating those.
Before writing my own DoF app I tested lots and lots in the market. There are only one or two that supports tilt at all, and I didn't find anyone that had the wedge-span-at-infinity concept which I personally think is quite important. When it comes to plain DoF apps there's a bunch (about 100 apps!), but 90% of them are disqualified as you can't configure the CoC. Of the remaining the user interface is often a bit cumbersome to navigate, and often lacking support of key workflows, like setting near and far limits and getting the focus distance rather than the other way around. I get the sense that many apps are written by good programmers but not being so familiar with the gear photographers use. In my app I chose the approach to make the configuration a bit more of an effort (such as setting up which camera and lenses you have), but once configured it's supposed to be smooth to use.
Most DoF apps are free though and my costs some money so it's not a fair comparison. I lacked a truly serious DoF app though and I gladly pay some money for apps that work than have 20 free apps that doesn't work as good. In photography I use two apps currently, my DoF app and a viewfinder app to plan shots before I unpack and place the camera.
(I discovered a small bug in v1.0.4, there's a feature to enter specific distance value (enable in settings, then tap the center row in the scroller) and if your lens is configured with nodal point separation like the ALPA lenses, that separation is added to the distance, so if you enter say 2.00 meters you get 2.02 for a wide angle lens with 20mm nodal point separation). I'll fix that to the next release, but I'll wait a while to see if something more turns up.)