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I use a combination of the logitech dinovo, ( its windows based, but have no issues) most often used is my MacBook pro via remote desktop. If you have an iPhone try hippo app.

For the majority of the time I find using my harmony one remote does everything. I can start stop Plex and control everything in Plex
 
When I first set up my mini htpc (a few years ago) I bought the logitech dinovo (I got the Mac version, though I didn't need to. It just happened to be available at a decent price on ebay at the time). To be honest, I haven't used it a single time in probably 2 1/2 years. It worked well when I needed it though. The few times I need cursor control/text entry I just use the free logitech iOS remote app.
 
Back when I had a HTPC I used a lighted Lenovo HTPC remote. It worked very well for that purpose but would not be ideal for general use with just the trackball for mouse navigation. But for a HTPC remote it was ideal.
 
I did buy the Apple wireless keyboard and mouse, but almost never use it. I just use my MacBook and use screen sharing to control the Mac Mini as it is much better this way. If you have a Mac laptop then my suggestion is to buy the cheapest wireless and mouse you can find for the rare occasion you need to use it. Most times you should use screen sharing.
 
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