I would like to suggest that he reveals the app to a small group in order to get feedback on how people like the app. He said that he released a similar online version and it got good results. I still think he should attempt to get feedback before he creates the app. Am I asking him to take an unnecessary step before launching
Many founders tend to view a product launch as a red carpet event that will get a ton of press coverage and huge social pickup. This isn't the case with 99% of companies. I've worked with hundreds of founders who expected a HUGE launch without testing product or building a set of customers ready for the product - only to find that most launches are inherently pretty uneventful. It's important to stay level and keep expectations for launch realistic, then build on what you learn and continue to grow your audience. The goal isn't to get an arbitrary number of customers on day 1 - it's to build a sustainable product with an audience that you know wants to buy it.
You can look at this two ways.
1. It doesn't really matter that your friend wants to launch the app, because the audience at launch is probably relatively small. You can use that audience to get feedback on it like you would on an MVP anyway.
2. if your friend has a big following around previous app launches, and launching a new app to that audience is a make-or-break scenario, then absolutely test with a portion of that audience beforehand. You can call them VIP's and give them early access, then hopefully count on them as your biggest supporters as you roll the app out to the larger audience. This gives you insight and gives them a feeling of exclusivity.
The equation of time vs. money is an important one. You don't want to sit on the app making changes for months, but you also don't want to come out guns blazing with the wrong product. Finding that balance is the most crucial point in your launch, and if the stakes are high with a big audience, definitely test it first. If the audience is small and can help give you feedback on the product, then a launch event probably won't have the potential blowback you envision. Best of luck!