Appoint is an ok tool, clearly in development but already with a good amount of functionality. For my however the big turnoff is the integration with Closely that you get for 'free'. But let's look at the app first.

UI
The UI is quite good. All has been neatly designed and well implemented. The app is in what I would call dark mode. I did not find a switch to brighten it up unfortunately. For me it's not convenient.

Setting up a calender
Configuring a calendar is nice and straightforward, no complaints there. The booking page could do with a few more options, like limiting the amounts of a specific call on a day. But I'm sure they'll be added in the future.

Integration
I did a setup with an O365 Mail and that went surprisingly well. That's a + for sure

Booking page
The customized booking page requires 2 codes (I only have 1). That's a pity. Especially because Appointly/Closely is promoted everywhere. Personally I don't like these kind of promotions. Especially not so prominent.

Other
After signing up my mailbox was flooded with Closely messages. At first I didn't understand where that came from as I didn't immediately activate my code. Now I now. Appoint is part of Closely which in turn is related to Leadrocks that also knows to find my inbox and upsell the brains out of you. No I don't like that kind of aggressive sales, sorry.
The product itself looks decent, but it's not for me. Good luck to the team for perfecting it however!