Which Dosing unit to buy?

[roblarss]

I've had a marine magic for about 8 or 9 months. i havent done a thing to it since. I did look at the other costlier units but this one does the job.
If i remember you can replace the motors/heads as they just pop out.
I did buy this off ebay so was wondering on the quality, but hey it does the job cheaply.