I have one a model older than this:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRST9&P=ML
Does a great job on my receiver packs, micro-t, cordless drill, transmitter, glow heater, 7.2V stick packs and 4 AA holders with NiMH's in it for my camera.
It's adjustable in .5A increments. I like to charge my AAA, AA, 2/3A (receiver packs) at .5A (500mah). Seems to give a longer lasting charge. Not as much punch at first as a 1A charge, but it does last longer. Takes a while longer to charge though.
The "ballpark" math on how long a charger takes is pretty easy to figure out. If your 6V 1200mah pack is completely dead, at a 1A charge rate, it will take 1.2 hours. If you charge it at .5A, it will take 2.4 hours.
With a good high quality receiver pack, you may be able to charge it at 1.5A-2A safely, but I like to charge slower to spare the battery. If you get too aggressive, it shortens the overall life of the cells. So, quick charge may cost you less time, but more $ more frequently due to the cells giving out.
I've been using the 1400mah receiver pack in my aftershock for almost 2 years. Still holds a good charge longer than I have yet to run it.
Considering the versatility of the MRC 960 I linked to, it's a great charger for many charging needs, not just RC specific stuff. If you can make a connector and the device holds 1-8 NiMH or NiCAD cells, you can use the MRC 960 to charge it.