@JUMA55 - I think you've had some real life experience with this one, no?
Kat, yes, the XTAR Dragon VP4 Plus is great for testing the capacity of batteries. Basically it charges them to full, then drains them, charges them back up and reports the mAh's. The unit can get hot and its ventilation is poor. It can also take a couple of days to do high capacity 18650's. When I'm testing, I put the unit in a cast-iron frying pan, raise it up a bit with a small stand since the vent is on the bottom and cover the pan when I'm not in the room with a lid from another frying pan. It's not a tight fit so there is some air circulation. Looks goofy but it works.
The Opus BT - C3100 V2.2 also does tests, but I don't feel it's as good for that as the Dragon. What the Opus does do better is refresh batteries that you think might be goners. Ventilation is better since the Opus has a fan on the back, but I still put it in the skillet.
But the best I think for day-to-day charging is the XTAR VP2 since it will charge at .25 amps. However, the Dragon does have a USB output so one can charge four batteries and one external mod with a built-in battery. I charge my Radii and JACs this way. The Dragon also has a LIPO out, which I've never used, and some probe gizmos that I've never used either.
I'm not Mooch and none of this is in any way any sort of expert knowledge, just opinion of a sucker that bought a bunch of chargers.