So this is definitely a great talking point - booking on the app. To book on the app it’s just ‘book’, and it doesn’t present the fields because you already know who the members are. This is a feature request and there was another thread that laid this out quite well. I forwarded that to the team.
As far as Spaces / Branded App… It really depends on your clients’ needs and what they want. There are advantages to using the app WITH a website. You can have both; you don’t necessarily have to choose between the two. =)