I used Dauntless for my ground instructor tests.
It was very good, not perfect. You have to choose which version you want at time of purchase: PC, iPad or Android. I would have liked a PC/iPad combo but they don't offer it. PC prices are a bit better and you can get a 3-pack deal. I went for the iPad as I valued the portability.
I like the fact that there's a study mode, which gives you the correct answer immediately, and a test mode that gives you the answers at the end, like the real test. The "question stack" thing is very nice, you can isolate questions you most often answer wrong vs ones you most often get right. I also liked the explanation that comes with each q/a, although the quality varied from simple PHAK quote to full walk-through with images.
Unfortunately there are a few mistakes (wrong answers), I was able to isolate them because I also had the Gleim book.
You should also look at these guys:
https://www.aviationexam.com/UI/Page...px?id=FAA_FULL
They also offer an iPad version, a friend of mine let me test it. Questions/answers/explanations are very similar, they don't have questions stacks. They are cheaper than Dauntless, $10 vs $30, but you only get access to the questions for 2 months. On Dauntless once you buy it, it's yours forever.
Overall I was satisfied with my choice of software+book, got 96 and 99 on the tests.