non stepper motor based dosing pumps

[david@rainess.com]

current stage I am at:
I have connected the kamoer dosing peristaltic pumps to the DC ports.  and tested that indeed I can control them via the reefpi.  they even can be switched on with less than 1 duration (0.5)  just like a "click".  I am about to start calibrating. Need to measure the required time per each pump for the required liquid volume.  

I have stumbled on one of the posts in the forum, that Rob is saying that using a non stepper motors like I do , will result in a non stable and not accurate dosing.
Is this really the experience that people have ? 

will my setup do what I need?  
I am talking about the usual add-ons that people use for reef. I have a 500l system so its not very sensitive like a nano. so a little more or less of the additive should not matter much. unless I am totally wrong here.  I am new to reefing...

thanks 
David