This native iTunes Connect client for macOS from Vadim Shpakovski is interesting. We all love a native app over working with a web page, and the collaboration features here look great. However, the power of this app will be in handling multiple iTunes Connect accounts. It's a common scenario for a lot of freelancers, and it's a real pain right now.
One thought I had looking at the site is that the pricing is quite bold at $60/$100 per year. If I had to give some advice, I'd probably suggest a tiered approach could work really well. For managing apps on one iTunes Connect account, charge something like $20 a year with the $60/$100 (or even more!) price being reserved for using it with two or more accounts. That way users get into the habit of using it, and spreading the word about it. But the real time savings from the app are going to come from managing multiple apps across multiple accounts, so charge the proper money for that. Anyway, these are just some random thoughts, the app looks promising either way!