Note: This reply is primarily copied from another comment I made comparing the TKey to another key.
I'm sure kfreds can provide a far more in-depth answer, but unlike the Librem Key, which (seems to) stores information locally that is then accessed and passed along to a device, there is no way of storing an application (or any other data) on a TKey. Rather, a device app must be loaded onto the TKey every time you plug it in.
Since each TKey device contains a Unique Device Secret, alongside it generating a hash of the application binary, and accepting an optional user-provided seed, it can derive key material unique to each application. If the exact same application and user-seed are provided each time, the application will return the same result.
This is, for example, how one can use the TKey for signing files and SSH. The generated public/private key pair will always be the same, without requiring any data to be stored.
Going back to your question, some of the differences include that: The TKey allows you to program and use your own applications, the TKey is fully open source (both HW and FW), there are no limits on the number of services the TKey can be used for, and the TKey uses USB C (meaning one can for example use it with a smartphone).
Note: This is a pretty basic description of the TKey, there's far more to it, but it should explain some of the difference!
I'm sure kfreds can provide a far more in-depth answer, but unlike the Librem Key, which (seems to) stores information locally that is then accessed and passed along to a device, there is no way of storing an application (or any other data) on a TKey. Rather, a device app must be loaded onto the TKey every time you plug it in.
Since each TKey device contains a Unique Device Secret, alongside it generating a hash of the application binary, and accepting an optional user-provided seed, it can derive key material unique to each application. If the exact same application and user-seed are provided each time, the application will return the same result.
This is, for example, how one can use the TKey for signing files and SSH. The generated public/private key pair will always be the same, without requiring any data to be stored.
Going back to your question, some of the differences include that: The TKey allows you to program and use your own applications, the TKey is fully open source (both HW and FW), there are no limits on the number of services the TKey can be used for, and the TKey uses USB C (meaning one can for example use it with a smartphone).
Note: This is a pretty basic description of the TKey, there's far more to it, but it should explain some of the difference!
//Disclosure: I currently work at Tillitis.