I haven't flown them myself, but I have read lots of bad stories about them on the transportation board. My friend is flying them from Seattle to Orlando in September. Originally it was supposed to stop in Cincinnati, with an hour layover before heading to Orlando. Now they changed it so that she flies into Atlanta, then flies up to Cincinnati
and then down to Orlando....the kicker is that her flight arrives in Cincinnati at 9:45am, and the flight to Orlando leaves at 9am! How on earth do they expect that to work???
She is calling this week to see about changing it, so I am not sure how it will all work out. I would suggest logging in and checking your flight once a week, just to keep on top of changes.
As to flying out of Buffalo, we always leave early too, just in case the border is busy, but crossing at 4 or 5am is never busy. We just use the extra time to have breakfast before parking at the airport. Security lines can be long in the morning, but the line does move fairly fast - and I imagine most of the flights leave a bit later, like 7, so it will be a snap.