I do allot of interior painting and when I cannot use a power sprayer I always use my Wagner Power Roller.
yes, it does save time, you never have to dip into the bucket and you are painting 100% of the time.
You do have to cut in though. It is just like rolling by hand. Normally, I cut the entire home then hook up my roller and just never stop. You can hook the hose into a one gallon bucket or into a 5 gallon bucket.
This unit comes with a shield so when doing ceilings, it will not splatter. They run about $150 or so and if you take the necessary care for it it will last you along time.
If you are just doing one small room, I would not break out this power roller as it will take longer to clean out the machine than to paint the room.
cleaning is one thing that you cannot skip on. it takes about 20 minutes when flushing out the unit to get it to disperse clear water.
I do think that you will enjoy it and its so user friendly on your back.