I run 3 Marine Magic dosers on 3 systems. They are both cheap and cheap
. I didn't have $1500 to spend on 3 good dosers so risked it with the cheap ones. They aren't flawless but they work well enough they have met my needs. I have to replace the tubing in the heads every few months and it is hard to find and intolerant of using wrong sized tubing. If the power goes out they retain the programming but not the time of day and they default to off. The motors are weak but work. If you are on a budget the Marine Magic doser will work for you but expect to have to check on it periodically (should do this anyway to check reservoirs) and replace a few parts every once in a while. Parts are cheap, ship free and customer service with them has been really good. Overall I would recommend them for somebody that is willing to put a bit of upkeep into them. Keep a spare motor, head, head tubing and tube adapters on hand (order along with the pump).
Dan