Cant help you on the keg stuff since I don't keg YET. But I can tell you I use a Johnson Controls A419 Temp Controller (digital controller) for my fermentation chamber....works great.
Now.....maybe some others can chime in on this....but, if the thermostat works on the fridge you shouldn't need a separate temp controller since you will be using it for kegs and keeping the beer temp within the normal refrigerator operating temps....i.e. not in the 60's like you would for fermenting an ale (which the fridge thermostat will not control to).
EVERYONE is entitled to my opinion!
Secondary: Chocolate milk Stout
Upcoming Brews: Dusseldorf Alt
Kegged: Biermuncher Centenniel Blonde