I have both the apex and Versa. I like them both but prefer the apex for dosing and the VERSA for AWC. I set the VERSA for continuous rate, no maximum dosage and no time frame. THat has been the only way it has been reliable. I will have it hooked into my apex to shut it off or on in case one of the pumps shuts off. That is the problem with VERSA. It doesn't do it automatically like the apex DOS> On the otherhand, it is very quiet and you can do very Large AWC very quietly. THe Apex DOS is super loud for anything more then 2.5 gallons a day.