will region 4 discs play well on US machines?
Yes...if it's region free. If it's not then you can properly crack it to play depending on what brand it is, theres various sites that have info about doing that. On some machines all you need is a little code that you enter with your remote, other machines requires a little more advanced work.
Another option is to play the dvd's on your computer, theres various software that makes your dvd region free and will allow you to play region 4 without any problems.
Another option is that you buy a region free player, a region 2 player (Europe) or a region 4 player. Region 2 and 4 can be played on the same player.
Personally I only buy region free players, a funny thing about it is that in Denmark the cheapest DVD players you can buy are the ones that are region free.