Recommendations

If the long term effects are cleared and is deemed to be safe for future health, this diet would be highly recommended.
The Fast Diet (5:2) requires you to count the calories you ingest on the 2 days of fasting. This would mean that you'd have to weigh and calculate manually the calories in each item of food, download an app on your smart phone and search for each food via the app or read the packet of packeted food and add up the calories they provide. This would mean a lot of time wasting during the days of fasting due to the calculations being time consuming and possibly confusing some some participants of the diet.
Therefore this diet would not be suitable for a long term diet or a lifestyle to follow. But, for a short term diet (couple of weeks - one month) or a diet to reach your goal weight, this diet would be very beneficial and a great diet to be able to reach your goal weight and improve the health of an individual. This diet could possibly be seen as a diet that can be used like a cleanse, maybe to it for one week per month just to improve health and keep a balanced and healthy weight.