As far as fast and relatively safe, I would say that keto diets work great if you can remain functional on trace carbs. I am a endo-mesomorph with a never ending appetite so the diet works great for me. But if someone was more towards the ectomorph side and only had a few pounds to lose, it might not be the best route to go. Also there are many ways to do a keto diet, but I choose to do one that closely resembles the Vince Gironda style. I have plenty of red meat in my diet, but I eat red meat and eggs earlier in the day and switch to chicken or lean pork, and by the end of the day it's fish or a shake. But not a fish shake, lol.
I found through trial and error that my body just loves to store carbs and get sluggish on them. So I will go 10 to 14 days on 20 to 35 grams of carbs and then have one day where I eat carbs but even then I don't get out of control with them maybe 150 grams or so. I just don't seem to need more than a couple servings of veggies or a hand full of berries in some home made yogurt.
I also am one of the lucky people in the world I guess, because I can handle all types of dairy and have no lactose issues at all. I hate to mention that here or any boards really because there seems to be milk and dairy product haters everywhere,lol. But it works for me and I would rather have a tall glass of milk, cottage cheese, yogurt, etc, over pasta, bread or taters any day.