The astrotrac special deal contains everything you need to get started with widefield imaging using a camera and a lens. It allows you to take longer exposures at longer focal lengths than a fixed tripod without star trailing. This means instead of just the moon and star trails, you can now capture fainter objects like galaxies, nebulae and the Milky Way. You can also use filters to cut out light pollution and bring out nebulosity, both of which require longer exposures. You can use lower ISO settings and achieve cleaner, higher quality images. Your choice of targets will be bigger and your images will be better.
The main advantages of the astrotrac are its fast setup time, small size and high accuracy. Polar alignment is quick with the polar scope and easy to understand (although I understand it's trickier in the southern hemisphere). The whole setup can be easily carried outdoors if you work in your garden, or it can be taken apart and transported to a dark site or taken on holiday. The astrotrac is very accurate when used unguided. The longest exposure you can achieve depends on the focal length, but two to four minutes is typical.
Still, the equipment here has its limits and when you run into them you will find that they are tricky to overcome. The longest focal length and exposure time you can get depend on accurate polar alignment. You can check and collimate the polar scope and its holder arm to improve things slightly, but trying for more than 400mm for 5 minutes will be frustrating. The geared head has a limited load capacity, so if you want to use a small telescope or heavy lens then the wedge and balanced head are essential.
I do all my imaging with the astrotrac and although I've bought more stuff for it since, it all started with the holiday special deal. If I wanted to take it to the next level with goto and autoguiding I'd have a much bigger mount with much longer setup time... no thanks! I'll stick with the elegance and accuracy of the astrotrac.
