Is there much of a difference/advantage with the double sided safety razor? Or is it just more convenient to have to blades?
your mean what's the benefit of having two sides? it's definitely not a deal-breaker, although it's nice to be able to flip sides of one gets loaded with soap/hair. you are rinsing off the thing constantly though, if you have a heavy beard it will be like 1-3 strokes on each razor edge then back to the sink.
as far as the double edge razor itself
advantages: cheaper in long run, less irritation if used properly, cool manly ritual, good smelling soaps
disadvantages: initially more expensive, easier to cut yourself, generally takes longer to shave