I think their UX is awful, and their client is very slow in channels with thousands of users. They should open up their protocol so alternative clients can be created, or at least some IRC gateway.
I haven't made many calls but the sound was always crisp.
Unfortunately you can't use these APIs to create third party clients because that violates their ToS, they are meant only for writing bots. If they catch you using these APIs with your full account credentials they'll ban your account.
Of course they can catch you if your client isn't 100% the same as the original there are going to be differences which "forensic" tools are going to prove.
Forensic net requests?
You can MITM the entire traffic. Mimicking it's nature isn't the hardest task in the world if all the data is handed on a silver platter, and it's even easier when their client code is uncompiled JavaScript. There are always people data mining the client.
If you're thinking they're going to check the actual software. Like ass I'm going to let someone into my house to check if I'm breaking their terms of service
I haven't made many calls but the sound was always crisp.