I have it.* I love the time chunking and divided my day into four categories and assign a task to one of them - then it is never assigned to the 'wrong' part of the day/I'm never auto-scheduled a task and think no, I can't do that now, I need to do something else. I also fitted those categories across multiple smaller chunks across the day depending on my concentration levels i.e. High concentration work is 10am-12pm and 2pm-4pm. 'Easy' work that takes no brain power is never scheduled during these hours.
I may be using it wrong but I'm not sure what the purpose of 'Projects' is - It would be more useful to me to have a check box to have just the tasks in one project displayed/scheduled on some days, but it seems that feature is only for grouping your tasks visually, nothing to do with scheduling. You can't even colour code tasks for different projects - they say instead you can just pick an emoji and put it in the task name to decipher between them, which is a horribly slow and clunky alternative. Just give me colours!
The way that you can split a longer task into shorter blocks and it will fit them in when you're free is pretty handy - but you must remember to tick off that block when it's done/roughly keep track if you decide you're on a roll and stay on it longer, because otherwise you'll have annoying 15 minute blocks scattered all over your calendar and no idea how many you really have left to do (probably a me problem tbf!)
Their support is a little weird. Idk what it is, I've never experienced this before. I'm pretty techy, and I'm always polite and friendly when I've needed to contact them. But their tone, no matter who replies, is pretty rude and dismissive and they speak to me as if the answer is completely obvious 
I find it really strange and I dread when there's a bug (which happens a bit too often - scheduling will get stuck and their knowledgebase is completely useless), and they are hands down the worst tool I use for customer service.
If you have a lot of tasks, be warned now that task creation is an utter PITA. Yes, you can create templates to streamline etc, but at a minimum, every task takes about 9 clicks to create - each opening up a new window which is slow to load etc. I really wish there was a bulk create feature using time/project/time block category templates and you could dump your task names in, with tick boxes to then select multiple from the list to change the task duration, priority to alter in bulk. But no, if you want to make a change, you have to open each one with a pop up window.
There's no way round this either. I connected it to Zapier and even worked out how to connect the API myself to a simple google sheets for task generation. Motion locked down my API privileges as soon as I got it going, and I had to contact them to lift it (even though my plan included API...). They then sent a chastising response basically saying 'We'll lift the block this time but we're not happy about it'. Obviously the API calls would be high at first to populate Motion with tasks, but ongoing it wouldn't have been as bad but I couldn't be bothered to email them with a 'Please sir, can I have some more' every day
I have looked at alternatives, but they all fall short of a feature I really need, so I haven't switched. If I'm brutally honest, I will at the first discovery of an AI scheduler that does what I want without making me feel like an idiot for asking a question. The key failing for me is managing tasks - the interface seems to be designed backwards with no easy way to mass edit. I could easily spend hours opening them one at a time to make changes, so you kind of realise it won't do what you want and adapt around it, which defeats the object of the whole tool.
*My work has changed in the last few months so I stopped using it and let the subscription expire, but I will be renewing it once the work goes back to normal in a few weeks time - if someone new hasn't come out with a better alternative!