From a mechanical perspective, I find the Dual mechanism to be delicate, and a bit fiddly. The ones I have worked on typically suffer from dried up grease, the bad steurpimpel, and a misadjusted power switch. Nothing outrageous to get in order. Frankly so far as changers go, I think a Garrard type A for example has a more robust mechanism, but the Dual no doubt has a way better tonearm and more sensitive trip. If you want to make it work automatically, it needs an overhaul, which isn't as time consuming as you may imagine, you just need to be patient and thorough. The manual is also useful info.
I'm no stranger to idler drives, I've had a Thorens 124 since the early 1990s, and I certainly have been thrilled with how it functions and sounds. I'm just curious what makes a Dual stand out, they do seem to have a very loyal following. Next time I get one to repair, I will put a good cartridge on it and take it more seriously. I am really becoming curious what all the fuss is about them. My opinion thus far has been hey the Germans made a changer which is better than say a Garrard or BSR, but it's no match for a Thorens or AR, or even good Pioneer.