You should consider that most other messengers offer no such promises, even vague ones.
I'd prefer a honest "We are no security experts, don't use this for critical conversations!"
They offer these 'challenges', but other than that? For me, this comment of yours would we something I'd agree with if
- Telegram would start out with a protocol that works/is 'accepted' (OTR, TextSecure)
- Would make chats encrypted by default/all the time
That'd be awesome. Given that they seem to know a bit about cross-platform development and design the result might be extremely interesting. Right now? I'm not convinced.
a) I hate the discoverability. Just because I install an app doesn't mean that my ex from ten years go should see that I'm online. Heck, my mom or aunt don't need to see me showing up in the address book either.
b) Desktop clients. Tablets with wifi only.