Your tank looks great. Your dosing does seem low, but as long as you are constant it is what it is. You have nice growth rings on some of your frags so they are growing at a reasonable pace. I personally am dosing 1.3 ml per gallon of tank water a day, which I think works out to a shade under 3 dkh a day, so you have some potential in your tank to pull down a lot more 2 part. I found in my system once everything stabilized/matured, that my two part consumption sky rocketed.
I have an aquamedic doser I used on my old calcium reactor and they are not good IMO. The can siphon depending on where the wheel stops turning. This could cause your two part to go into your tank uncontrolled, or the reverse scenario with air or water back siphoning. True, you could set all the tubing at the right height so it does not siphon into your tank, but honestly it is not worth it. I would go Bubble magus, or if you want individual control with a separate controller, then a BRS pump as they do not siphon. You really can't beat the value of the bubble magus, and if you want to automate more dosing later it is easy to expand. My .02.