The Logitech Harmony Ultimate has two methods of communicating with an Apple TV - IR and Bluetooth. If you use the Smart Keyboard with infrared, you're limited to the commands that the old-style Apple Remote is capable of, ie: Directions, Select, Back, Home and that's about it.
To be perfectly clear: TEXT ENTRY IS NOT SUPPORTED VIA INFRARED WITH LOGITECH HARMONY ULTIMATE SMART KEYBOARD.
I had the Smart Keyboard shipped from the US because you can't buy them in Australia, and it's fantastic. The beauty of it is that it automatically switches to the device you're using. I can control a PC and an Xbox via the two supplied USB dongles, and a PlayStation & Apple TV gen3 via Bluetooth. One keyboard, every device. Awesome.
Apple TV gen 4 does NOT support this. In fact, Apple TV Gen 4 is the ONLY Apple device released in the past few years that uses text entry, but doesn't support ANY external text entry method. Ipads, Ipods, Macs, Macbooks, iPhones, previous gen Apple TV, you name it, they ALL work with Bluetooth &/or Remote App in iOS. But this one doesn't.
And, it's THREE TIMES the price of the previous generation ($AU, for 64Gb model that I purchased). This is the first time, ever, that I've been disappointed with an Apple Device I've purchased.