I lived with a power venter on an oil fired boiler for 10 years. I got it because it was cheaper and I didn't want to give up the floor space that a chimney would take. It worked great for a couple of months, then started to vibrate. Soot would collect on the squirril cage fan & throw it off balance. So, for 10 years, every 8 or 9 months I'd have to take it apart & clean the fan. Not an easy job at all. Eventually we put an addition on the house & it covered the power venter so I did away with it and had a chimney built. I wish now I'd skipped living room carpet & used that money for a chimney. After the chimney went on line my electric bill dropped about $10 a month.
That being said, and noting that a direct vent is a different animal than a powerventer, unless you NEED a powerventer, get yourself a chimney. If you're adding coal and want the old oil unit as a back up I guess a power venter wouldn't be a bad idea for the oil because it wouldn't be used too much. Hey! I think that's the answer! A power venter is a good item if it's not used.