I’ve owned a Pixio since 2016 and a Pivo since last year so I’ll comment on those two. It’s very important to understand the situations in which you’ll be using them in order to understand which one is best for you, because they both have benefits and drawbacks.
Pixio is a 5 piece system that is dependent on a robot, a camera (video or phone), three rail beacons that get placed on the rail around the area you’re riding in (tough for XC) and a tracking beacon that you wear on your person while riding. This makes it extremely accurate, and means it is able to track a single horse among a group of horses. It also makes it finicky (sometimes it doesn’t work for seemingly no reason) and a pain in the butt to set up, which I wrote a blog post about: https://www.cobjockey.com/2018/01/how-to-set-up-pixio.html The Pixio components have not held up well over the five years I’ve owned it, with all three rail beacons requiring external battery packs, the tracking beacon needing replaced once, and the charging ports getting loose on all of the rail beacons.
Pivo is a one piece system that uses artificial intelligence to follow a horse shape around the ring. This makes it dead simple to set up and use, but means that it cannot track a single horse in a group of horses, nor is it ever likely to be able to do that, so if you regularly ride in company, a Pivo is not for you. Pivo also does sometimes lose the horse shape, and is very YMMV on how well it works with your phone or not, so if you need flawless recording, keep that in mind. You absolutely need a newer (2018+ish) smartphone with a fast processor and a good battery, but you do not need signal of any kind (besides Bluetooth, which is what it uses to communicate). Range sucks on the Pivo compared to Pixio (better) and Soloshot (best) and it would not be good for XC, the horse shape it’s following gets too small for it to detect.
FWIW, I have completely stopped using my Pixio in favor of the Pivo, and I also take virtual lessons through my Pivo weekly with great results. It’s just so simple to use and works MOST of the time, I can’t bring myself to drag the Pixio out anymore.