Rumor has it Sigma is coming out with a new 150-600 lens to compete with Tamron's offering in that focal range. They must be trying to move inventory on the old ones. I've had this lens for about four years, and even though it's been in the shop twice, I've been very pleased with it for wildlife photography. However, it is not light or great for going on hikes. I wouldn't go more than a couple miles with it, and absolutely not in difficult terrain.