I was thinking of the stand alone Kamoer dosing pump this Black Friday. It's a 3 head version for $300. Seems like it would be reliable and not as expensive as Vertex or GHL. I didn't like the GHL because using it is dependent upon connecting it to a PC.
You only need to connect to PC to set up, after that, it's all cloud based. I'm with you on the PC thing (being an all mac house) but fortunately I bought my son a pc laptop for school work and lucked out. If you don't have a pc, maybe you can borrow one for the initial setup? Also, GHL makes a 3 pump version, but you'll soon discover that having an extra pump isn't a bad thing, especially if one goes down (very rare), you can move your programming to the unused pump until you get a replacement. I like redundancy myself. The other thing about the standalone doser, you can add a temp probe and ph probe with the expansion port. There's level sensor(s) ports, stirrer port(s), etc..... They package a lot under the hood.
Just saying. Good luck!