So to pick off a few points (you likely know, but more for any newbies reading the thread):
1) Low carb / keto while on medications with risk of hypos, or insulin - this should only be done with your doctor's full knowledge, monitoring, and medication dosage alterations to compensate for lower carb intake. It's not something I, or this forum that I've seen, recommends be done without that in place. I'd also add that I'd recommend anyone considering a drastic change in diet/lifestyle only do so with the full knowledge of their doctor.
2) Ketones - If you're in nutritional ketosis, generally speaking then ketones should be used by your body for energy. You shouldn't have a build up in your bloodstream as such because they're used as fuel when carbohydrate isn't a readily available dietary energy source. It's why the keto fanboys on Reddit, pushing that they test to see if they're in ketosis, are generally just wasting their money on urine strips and expensive blood monitors for ketones, then stressing that their levels are low. They're probably low because these people are in ketosis and their body is using ketones for fuel. However, if point 1 above is followed, this can monitor for any issues and catch any circumstances where this "general" rule doesn't apply to someone's physiology.
3) Benefits of nutritional ketosis - For me, the main problem here is misunderstanding the purposes of ketosis. Ketosis itself doesn't control blood glucose, or result in weight loss directly. Lowering carb intake helps control blood glucose, whether that's down to keto levels of intake is up to the individual. Ketosis helps lower appetite, so an indirect consequence is weight loss through lower overall consumption, plus fewer cravings for carb based foods. In addition, some studies have shown that the keto diet promotes visceral fat loss in the short term, which is important when it comes to conditions related to diabetes, e.g. fatty liver, insulin resistance, lower pancreatic function etc. Overall though, studies show that weight loss can be achieved on any diet, of any model, and longer term the initial benefits of keto on visceral fat are also seen on other diet models too. For me personally, the lower appetite and cravings in ketosis definitely help me to maintain my diet, weight loss, and blood glucose control.
Some links to studies/articles I've found (usual disclaimer - I'm not a doctor, nutritionist, or a scientist, my understanding may be incorrect):
Introduction The ketogenic diet is a diet that relies on reducing carbohydrate intake to a minimum while increasing fat intake. This induces a state of ketosis where it is hypothesized to favor fat metabolism for energy instead of carbohydrates. The ...
Although various studies have examined the short-term effects of a ketogenic diet in reducing weight in obese patients, its long-term effects on various physical and biochemical parameters are not known. To determine the effects of a 24-week ...
The appetite suppressant effect of ketogenic diets may be an important asset for improving adherence to energy restricted diets and weight loss outcomes.
Ketogenic diet is an effective treatment for nonalcoholic fatty liver disease (NAFLD). Here, we present evidence that hepatic mitochondrial fluxes and redox state are markedly altered during ketogenic diet-induced reversal of NAFLD in humans. ...
There are more, however these sum up the majority of what I found during researching keto.
Overall, as
@Spirit01 has very eloquently outlined in posts on this thread, it's down to individual goals, motivations, and preferences as to whether a keto diet is suitable. Some may also have medical reasons and/or conditions that don't make it suitable. However, for many people, it can have some real benefits for glycemic control and weight management.