[ZoranC]

Both methods of oil changing (draining vs. extraction) have pros and cons. Problem with draining is that you do not get all the sludge and remnants of old oil in the system out. Problem with extraction is that ... well ... you get more sludge but not all remnants of the old oil in the system out. In either case you do not want all remnants of the old oil in the system out as you do not have a way of completely priming the system with new oil before you crank the car up.

I feel combination of both methods together with quick run of clean cheap oil in between once in a while is the best way to clean the system. What I mean is when you are ready for oil change you extract oil and sludge using vacuum and fill with inexpensive oil that you run on for a day. That dilutes rest of old oil and dirt in the system. Next day you drain that and put in your regular oil. I feel that way you got more out.

If I was doing this as sole method I would not do it without relocation of oil filter.

BTW, this one seems to be based on Mityvac unit. Mityvac also has ones that work off air compressor. Should be much more efficient extraction.

EDIT: Even if one decides to solely drain it is good to have one of these units. Once in a while you have a need to make longer trip on short notice and it is usually when you do not have time to change oil by draining (or some of us do not have a place to change oil) but your oil does need change. Quickly extracting majority of oil and replacing it with fresh one gives you a band aid with decent safety margin (assuming your oil filter is not on it's last legs).