They are very popular out here on the West Coast, particularly down in the state of Washington. I have read that they are very well made. Like all welded aluminum boats, however, they command very high prices, which are probably justified based on the sheer durability and lifespan of aluminum hulls.
Of what they call the "cookie cutter" welded boats, all of the major brands are probably very good. Based on what I've read, North River is very near the top of that list. For a little bit more money, you could look at Silver Streak, Lifetimer, Northwest Aluminum Craft or Eaglecraft, which are Canadian custom welded aluminum boat builders. There are some very good custom builders in the US as well, both in Washington and Oregon. The ones I mentioned all have websites, with the possible exception of Northwest. Those along with the "cookie-cutter" welded boat websites will give you a really good idea of what's out there.