Both are controllable, they are almost identical in every respect, a 6101 can act as both a 6000 and 6100 by changing a jumper and it just has fewer parts. Basically on the pro side the 6101 is neater (fewer components) and more adjustable (6000 and 6100 in one), on the con side the 6101 is more expensive to repair outside of warranty, one $180 part replaced 2 $90 parts.