Have a look at the Discord channel where the users complain about the problems. It certainly promises to be something good, with a wide range of voice types but there is much to be improved for classical singing. It's $10/month, lifetime licence $149 is good value if you intend to go on using it.
A cheaper alternative is cantamus.app at €5/month but limited to one voice per staff. Adequate for its stated function of preparing rehearsal tracks for singers, not a synthesised choir which is the aim of Cantai.
Yes, it's the community discussion board. Cantai don't provide support there, any more than Cantamus do on their Discord channel. It'll only cost $10 to try Cantai for a month to see does it work with your specific music and desired voice types. You'll probably need to sign up (free) to their Discord channel to post problems and get the workarounds from those who have been there before.
I did the trial … went back-and-forth with support… they have a lot of bugs to work out. However, it sounds really great for choral music in the Roman Catholic tradition.
I have it (was an early supporter for 2 years before a product dropped) but as of yet don't use it much. There are still rough edges. The good news is that development is happening at a breack-neck pace, and it is getting better. Early iterations had vibrato that would have made a billy goat blush. Recent choir voices have toned that way back (thank God). But there are still issues being worked out.
@francis, I suggest you put that point on their Discord channel and see if you get any ideas to try. I'm not following it closely but people are constantly coming across and overcoming limitations and where that fails submitting bug reports.
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