I found that when I have the iPad Pro connected to an external monitor and I use the Magic Keyboard and Trackpad as my input device, I end up staring at the iPad Pro's screen instead of the bigger screen. So, to force myself to remember to look at the monitor, I move the iPad Pro off to the side on a stand (more on that in a minute) and use a wireless keyboard and trackpad.
The keyboard I've been using for the last few months is Logitech's MX Keys for Mac. I'm not a huge fan of the size of the keyboard — I'd love a TKL version of this keyboard that lacks the number pad — but I've grown fond of the battery life, and the layout that's specific to the Mac, which translates to being specific to the iPad.
The only thing I don't like about this keyboard is that not all of the media keys trigger actions on the iPad Pro. For example, the play/pause button works, but the track forward and back keys don't do anything. The same goes for the mute/unmute key — it works — but the volume up/down keys don't do anything.
Logitech does make a $99 TKL version called the MX Keys Mini for Mac but I haven't used it yet.