What do you think of the proposition to switch to another messenger?
I’d say: “Switch to another messenger? Oh no!”
The advantage of Delta Chat is that you don’t need to make this proposition to your friends, you would ask them their e-mails and start chatting with them.
So why the invitation (Settings / Invite Friends) has the proposition to switch to Delta Chat?
Wouldn’t it sound better if the custom message was a tip to use your existing e-mail in a whatsapp / telegram style?
I imagine it would be a more direct way to speak and it would make your friends wonder "how to use e-mail as if it was whatsapp[?]".
Settings / Invite Friends: “Tip: use your e-mail in a whatsapp style with Delta Chat - https://delta.chat - [email@example.com]”
Settings / Invite Friends: “Let’s switch to Delta Chat - https://delta.chat - you can text me at [firstname.lastname@example.org]”
I’d also suggest that the above text could be used too as default signature text, with proper modifications. BTW, feel free to suggest better texts, as I’m not a native English speaker.