The remote itself can do up to four devices, including the TV. Some of the higher end models control more devices, and add a LCD screen, macro options and a few other options. Now this is HDTech speaking personally, and not speaking for Logitech or Samsung, so strictly unofficial.
If you're looking for device compatibility, you can list your devices on their website and see if they match up prior to purchasing. Click on "Device Compatibility" on this link:
I bought mine because a replacement remote for my 9 year old Teac receiver was over $100. I saw a few posts here about Harmony remotes, and got one for, I think $30. online for the receiver, and to play around with to see if it matched the hype. I was pleasantly surprised, since it worked with everything in my setup (though, I didn't test the game consoles), and I'd have been happy if it just turned on and changed the volume of the Teac.
One other caveat - some buttons on some remotes aren't duplicated on any universal. Like if the Comcast remote has a special "Buy" button for movies, or has odd buttons not found on a typical remote, you may be able to interchange buttons, but then you'll have to memorize what you changed. Every now and then, I still have to reach for the original remote, but not often.
There is a little bit of a learning curve - for all my inputs, I had to program the volume button on every choice to the receiver. So I could be on TV mode, and the volume button would normally control the TV's volume, but I wanted it to control the receiver EVERY time the volume button was pushed, so I had to input that into the software setup interface, which was pretty easy. And so on DVD/Blu-Ray buttom mode, and I had to again tell the volume buttons again to control the receiver. But in less than 30 minutes out of the box (and I'm a bit of a geek, so depending on your tech level, discount accordingly), my solution was up and running. It's not something to impress my friends with (basic, no screen, no frills, and the design is a bit boring), but it gets the job done - again - in my personal opinion.
Hope that helps.