I don't think that the teacher asking her to use a SLR was really a reflection on the QL17 - rather on the fact that in a intro class, the fewer variables you have with people who have little or no knowledge of the subject - the better. I believe any rangefinder would meet similar fate.
Is it special? My wife and I love ours - its solid, has a very sharp, fast lens. Perfect for street type photography (40mm focal), it has a coupled rangefinder and fast flash synch.
I think the allure is that it offers most of the adventages of the RF's in general while not costing nearly as much as some, and being very close rival in quality to most and better than many. That's all, really. I would not trade mine for twice as much as I paid for it! Having said that, its an RF with one lens and all the inherent limitations of that set up, so I don't know that I would go as far as saying its the best all around camera - an SLR is much more flexible in many ways, obviously. But if you want a small, wellmade, fast focusing, whisper quiet 35mm camera with a slightly wider angle lens I can't think of more bang for your buck. And the meter oly works in Auto mode - you can switch to auto, meter and then go full manual if you wish. The meter is... well, its a bit of guideline, really - but its useable.
PS - isn't the petri a half frame camera? or is it just some models? the Canonets are full frame 35mm, and the 17 especially is about as compact as you get this side of a Rollei 35mm - and its a more capable camera from what I can see.