Have a friend looking at a top-break revolver and he asked me if I knew of any disadvantages of this design. I honestly do not know but thought that I would ask here...Advantages? Disadvantages?

The advantages are simultaneous ejection/fast reloading, especially on horseback. The disadvantage is this is a 19th Century design and lacks the strength for todays high pressure cartridges. Within its limitations though it was very effective in its day. Do a little research on the .455 Manstopper loading for the British Webley for an education in terminal ballistics.

I think they are a cool design myself, they are usually chambered for the .45 Scholfield which is shorter than the Colt cartridge (this is reason you here the term .45 long Colt, to differentiate it from the shorter.45 Scholfield ) and also the .44 Russian I believe.

There is a modern Russian .357 magnum top break polymer revolver. I don't know if it ever made it to production or if it was too weak or something.

http://world.guns.ru/handguns/hg49-e.htm

It would be awesome if that gun can actually handle that caliber and was for sale.