I had a HUGE post typed out here and then lost all of it. I'm not typing the whole thing again so this is a summery, LOL.
I agree with Laurelin. A sheltie is a unique dog and not for everybody. I don't think anybody would disagree that a border collie is not a dog for everybody; neither, then, is a dog that has it's roots in the border collie breed. It shouldn't be surprising.
Yes, they are definitely very quirky and unique dogs. Auggie is certainly not a neurotic mess; my sister has two and one of them I would say yes, he is a real mess. There is just something not right with Happy. I love him all the same, I'm just saying. Kota, on the other hand, was a rescue that we believe was abused, and outside of his extreme fear response (he will tremble visibly and frantically offer his paw in appeasement if he even suspects anybody is unhappy) he is actually a very nice dog.
I typed up a bunch of snippets from the book Sheltie Talk but I don't want to type those up again either, LOL. The fact of the matter is that the kind of dog the book talks about and the kind of dog Auggie is, those are not the dogs that you find most today. The book even says it's difficult, at best, to find a dog with the proper old sheltie character, but that once you have found it an experienced it you will never want to settle for less. THAT is 100% true.
It comes down to what the breed has become in the hands of shoddy breeders and owners who have no idea what a sheltie should be or how to handle one as well as breeders who are only concerned with coat and are not concerned (or as concerned) with temperament and working ability. I honestly think if a lot of people on this board met Auggie, you would be surprised at how far he is from the public perception of a sheltie. I am told all the time in public things like "Oh, he's so friendly! Aren't they supposed to be shy?"
I am EXTREMELY blessed to have found Auggie's breeder. Anybody who is looking for a sheltie puppy should do their best to find a copy of Sheltie Talk (it's out of print so you'll have to buy it off ebay or something) and really read Chapter 2 to get a good handle on what a sheltie should be like... and then do everything in your power to find a breeder producing those kinds of dogs. I just described Auggie last night to a co-worker as "a very balls-to-the-wall kind of dog." He is tough, nervy, drivey, smart as a whip, and hilarious. I always have to be one step ahead of him or the results will be really, really bad, LOL.
Do I think neurotic shelties are the norm? No, but I think they are definitely increasingly common. I think it's a result of poor breeding practices and popularity of a breed that is not an "every person" kind of dog, so as Laurelin said, you get dogs that haven't been socialized properly or handled properly... people who have no clue what they're getting into with a sheltie so they end up with a neurotic dog because they unknowingly encouraged the neuroticisms.
I absolutely wouldn't say that a sheltie is a high-risk potential biter. And yeah, Happy has bitten me before. But Auggie is nearly four and has never once even bared his teeth in a snarl.
Honestly, I would say that if you adopt a sheltie you should be prepared for some neurotic behaviours. It's not a guarantee, you just need to be prepared for it and make sure you have a great resource for working through things. If you want a puppy, be prepared for a lot of hard legwork to find an excellent one.
I think herding dogs on the whole can be a challenge and the sheltie is no different in that respect, they just have their own unique qualities. I think any and all herding breed has it's own unique qualities/challenges no matter if it's an Aussie, a sheltie, a border collie, a GSD, et cetera.
ETA: LMAO and it's still a huge post either way.