They are not as common as the short chassis and were only made for a aesthetic reasons. Mesa wanted them to not look so small when sitting on a 4X12. There are a few guys here on the board who one one, BigMouth's is a flawless Simul Coliseum hardwood. They are a joy to work on compared to the short chassis. Ahh, room. From a purchase standpoint, they do not sell for any more or less than a short chassis.
Happy Trails.