Well, if your TV is anything like my UN40EH5300, the Logitech K400 will work with the web-browser app. It will provide the ability to move the cursor via the trackpad and select hyperlinks. It works decently, although the WebB Browser, at least on my TV has a tendency to run out of memory and crash...
So you will probably find the keyboard doesn't work with Netflix, Amazon Instant Video or Youtube as you might expect. At this time, and I suspect this is true of many models, you cannot use the keyboard to type characters in the respective application's search field, which is a real shame.
The usability issue of having to resort to the cursor keys on the TV remote is significant.
Back to the Web browser, another annoyance - specifically when using the K400, at least with my TV, there is no way to disable the pop-up virtual on-screen keyboard that is displayed for those needing to use their remote for entering characters. Oh my.
Here's an example of an application on the TV that actually uses an external keyboard... but then it is not SMART enough to have been programmed to provide a setting for SMART customers to disable the popup keyboard.
In some ways, this lack of keyboard integration is disturbing. The SMART HUB vision IMHO isn't fully productized. The quality of these apps, the lack of keyboard integration and simple logical features like the one I describe above suggest SAMSUNG needs to do quite a bit more to improve it's product line in very fundamental ways. Certainly it has the programming expertise to make this happen.