you mean this?

Mostly the brand, design and price. Other than that, they are the same with generic NFC tags.

Tectiles are using Mifare Classic chip with 1k memory
Sony Smarttags are using Ultralight with 64 bytes memory

Oh, if you like the Sony smart connect app, you can use it with any NFC tag (not necessarily Sony's) by just writing some code on it.

You mean link credit card with your NFC-enabled phone? Nope, not yet.

Yes, mifare classic hack is well known. No known security issue with DESFire cards (4k and 8k) cards yet.
But those encryption stuff is for use cases like payment cards, transportation cards etc. Theoretically, you can make use of the encryption to protect your data, but I do not know any Android app that make use of these encryption yet. Perhaps the SDK does not support it.

For typical usage of NFC tags with NDEF data, there is no encryption. The 'lock' that you see is to lock the tag to become read-only. Anybody can read the tag, just that they cannot overwrite it once it is locked. This scenario is useful for NFC smart poster in public area. You don't want somebody to overwrite your URL to point to an adult site for example.

The lock is permanent. Even you yourself cannot unlock it.