I’ve done a couple rounds of FMD Prolon which is supposed to have the same benefits as straight fasting. I found sticking to low calories much more difficult than water fasting. With low calories you’re never satisfied and spend a lot of time thinking about when you can next eat. With water fasting it’s like you accept that you won’t be eating and it just feels easier.
My understanding is that VLCD will cause your body to down-regulate your energy expenditure long-term (this is why all but one of the folks who did The Biggest Loser gained the weight back). Fasting doesn’t induce that adaptation; if anything, it may cause the body to increase its energy expenditure.