In general, shakes are allowed with Gymondo, but are not a must. They should contain few additives (short list of ingredients) and be low in carbs. There are drastic differences in the amount of carbs in some of the products out there. Some shakes has just 3.4 g of carbs for every 100 g serving and are therefore low-carb and suitable for your diet, while others might have up to 25 g of carbs per 100 g serving and are clearly off the charts. In terms of price, shakes with a high protein content are generally more expensive.
Nevertheless, your diet should consist largely of fresh, healthy foods.
The best-case scenario is to make your own shakes and only as a supplement to a balanced diet or as an optional, additional meal when you are building muscle.