Im big on dual stage units as they help bring the pH back up before it goes back in the tank, letting u melt the media in the 1st chamber w/o worries and more efficiently.
That said, I bought an MRC CR2 due to there great customer service and great build quality and relatively low price compared to these 1 stage deltecs $$$
They are pretty straight forward as well w/o unnecessary bells and whistles (such as secondary bubble counters and internal pH monitor sockets)
I have ARM media and Zeo Mg granules, this keep my tank at 1400Mg, 430Ca, 8.5 Alk, Sr 10 and for my water volume I have a high Ca/Alk/Mg load. I couldnt keep up w/ kalk/vinegar solution everyday w/o shooting off my PH