You are going to get conflicting opinions on this because two hobbyist will use the same product but have different experiences. Then you have to factor in who comes to forums to post more often. Those having issues and frustrated vs those not skipping a beat.
Controllers are not necessary. They are a quality of life improvement when designed properly. Redundancy is important with, or without, a controller. Something to keep in mind. Another thing to consider is the support location and country.
Dosing 2 part, single part, or amino acids is a no brainer for most controllers with dosing pumps. See comment above about redundancy and safety checks. You can add logic to limit, reduce, and notify should hobbyist or equipment go oops.
Above all, regardless of brand, test it before implementing. Easy to do by using buckets.