I have! About a year ago -- it has great library management, and is overall a very good effort that could take over KiCad's place over the next decade if they stagnate.
My criticism is mainly that the PCB layout tools were still buggy. I believe it is/was using some of KiCad's router code, but it took more work to get a layout done than doing the same thing in KiCad would. It also tended to get glitchy with increasing layout complexity. The schematic editor is a lot slower than KiCad's and not as feature-rich.
The GTK widgets look and work very nicely on gnome-based environments but have issues on kde / windows. To be fair that's a GTK issue and not a Horizon issue, but unless Horizon has changed a lot lately I'd have a hard time recommending it over KiCad right now for professional use.
