I've heard two things:
1. Because everything is small, including the tanks, you can't get enough heat to do heavy stuff. Don't plan on brazing any castings with it.
2. The tanks are small and have a fairly short life. Always keep a spare set in stock.
Other than that, they are pretty good and sure have the edge in portability. My big tanks live in the corner of my garage and I have long hoses because the tanks are difficult to move without a cart built for that purpose and that takes up too much space for me.