I don't use Telegram for anything that requires "real security", and advise against doing so. I assume that 100% of what I say in Telegram would be accessible to whatever authorities there are. I only assume that low-skill script kiddies won't be able to read my encrypted chats. I use Telegram the way I would use Facebook, or post-it notes in an office coffee point: with no expectation of real privacy.

It still covers a lot of mundane communication cases.