I'm actually looking around for courses/textbooks at the moment. I'd say the things I'm looking for are:
- Speaking practice and a focus on getting OK pronunciation early. At least according to the German Discord, it's important to get pronunciation correct from the start. If you don't it becomes very difficult to break bad habits across many hundreds of words.
- Effectiveness over dogma: I would prefer a course that focuses on teaching effectively through multiple different methods rather than being hyperfocused on one of them. If your secret is really as good as you claim you might not need this, but I'm sceptical.
- Practical vocabulary. Duolingo etc have a reputation for teaching you absolutely useless words and phrases. Particularly at the start it would be useful to beeline for a target, be that "get by on holiday" or "have a conversation with another learner/a native simplifying their language".
- Spaced repetition. I'm using Anki, but the decks aren't very good. Spaced repetition is basically a cheat code to learning, and if you integrate a good algorithm it will absolutely differentiate a course.
- Cost. I'm a student doing this in my free time. I don't want to spend lots of money, particularly when there are lots of good resources already out there. Why buy this over just using the many available resources? You have to offer something.
- Realism. I'd prefer "Learn in one year, one hour a day" that is truthful and realistic to "Learn in 3 months 10 minutes a day!" because I just know that that's untrue.
- CEFR alignment. It just makes things easier.
- Corniness gets on my nerves. Some videos are alright but please don't try to act.
I would recommend going into language learning communities - reddit, discord, etc - to see what they're looking for. You'd also benefit a lot from sharing some more details about your course.