The KhD from GHL is great you’ll Love it along with the 2.1 SA . KhD Very accurate. The directions aren’t to clear at least not when I had to set mine up (almost a year ago ) just make sure you keep the bottle of reagent right next to it so the tube isn’t long , and to prime the tubing or the tubes can shoot off , but after it’s up and running it’s nice . I like GHL (looks way better ) but Apex is little more user friendly and that I cant use on phone while away from the house , I think people have set up port forwarding though but I haven’t messed with it , also downside is for me they’re not in America