Don’t discount GHL. They have the doser, KH director which measures dkh and doses to keep it within your parameters. The also have Ion director coming out that will test calc and mag and possibly nitrates!
Reefbot is good for testing only then you need to correct dosage on your own.
I don’t know enough about apex but it is a lot of plastic parts. Plus the trident needs to be returned every couple yrs for a tune up. That doesn’t sound good to me.
I just got the GHL Doser 2.1 and am looking to expand into there other products.
I use both the KH Director and ReefBot, and I can honestly say that I can count on the ReefBot more than the KH Director. The KH Director can give accurate results but it seems every now and then I have to either vent the reagent tube or flush the measurement cell. I especially have to do that multiple times every time I use a new reagent bottle. The KH Director does let you use a longer inlet tube than the ReefBot (the ReefBot can go up to 2 meters) which means you will need to keep the ReefBot close to tour aquarium.