I think not using a mobile number would be much better. Also it is not available only for Desktop. That's it, nothing else.
Signal does not require you to use your phone number
most people don’t realize is that Signal “phone numbers” are not really phone numbers.
You can link Signal Desktop to your mobile device to send and receive Signal messages from your laptop or desktop computer.
I maybe wrong and probably signal is best one out there. In fact i am using it now and i can say it is the best one."other":
In windows store you can load "Unigram" which is Telegram client as AppContainer! Sadly the official isn't.
Also I wonder why the survey include Signal if you search for alternative.