This was the second of Canon's A-series cameras to come out, the little brother to the AE-1. For many years, Canon liked to introduce important new cameras in pairs: there was the big, full-featured one and a lesser, more conservative model. This was the latter.
Basically it's an AE-1 without the automatic exposure capability, and instead of having that nice needle with the aperture scale in the viewfinder, it just had the old match-needle system. For this you saved about $50, and Canon figured this would appeal.
Maybe it did, but the AE-1 sold huge and the AT-1 didn't. Obviously some of them sold because I see them from time to time. But the AE-1 had full-manual mode too, all you had to do was take the aperture ring off the A setting, and suddenly you have an AT-1. So I don't really understand what Canon was trying to do.
That said, I always wanted one and never understood why. I had an AE-1 which I loved. A friend lent me her AT-1 and I used it and hated that the match-needle. But still I liked it. And I wanted one. But I didn't want to pay much because really, it doesn't offer me anything that I don't already have. It's just filling an empty spot in my collection.
So I got a broken one. The shutter works but the film advance is jammed. I've got a repair manual so I may try to open it up and see. As I'll probably never run a roll of film through it, it doesn't matter a whole lot what happens.
For more information: Canon Camera Museum
Camera manual: Orphan Cameras.com