The Demand service is the same as buying off of disc, any problems that aren't inherent with being a disc will be on the Demand version as well.
Also, check prices first - is buying it from the store the same or similar price as buying on Demand? And if Demand is more, is it really worth it for you to not have to get off your ass to change discs and keep up with cases? Just some questions to make sure it's the right decisions. I've bought a few games from Demand and sometimes think I should have gotten the case, booklet, and disc.