ESP8266 Community Forum

You misunderstood me. I don't think you shouldn't do it, but I think you will encounter limits very often (like this one).

Also the question arises how safe it really is, having some corners cut here and there probably.

I would say it's as safe/unsafe as any other implementation - the protocol is standard, mbedtls is public and so well scrutinised for holes, and if you choose a good cypher suite, at least 2048 bit keys, SHA256 or better signatures, TLS 1.2+, and avoid known issues (like SSL3 which they recently re-enabled in the code and I promptly disabled again) you are as safe as anybody else.