It's Europe biggest Lake called Balaton. Water along the south shore is flat or choppy. If you go upwind, deeper into the see you may encounter 1m waves. Shallow for about 250m, with 10-70cm depth. You can launch and land in the water. The lake bottom are covered with sand (silt). The lake is only 3-5 kilometers wide, so there is no danger of getting lost.
The beach 500m long and 60m deep, covered with grass. The beach is quite busy and not so big, therefore it's quite difficult to launch and land the kite. Beach is mostly grass, with some rocks as coast protection. Some trees and buildings on the beach but wide enough to launch relatively safely. Exits/entries are through stairs or rocks.
The season starts from April to around October. The summertime (June to August) is quite hot around 35-40°C. The water is very hot 25-28°C. Only shorts needed. Autumn and spring the air is colder with 17-25°C, the water is 15-20°C. Wetsuit is needed because the wind can be colder.
Usually the wind blows when a cold front is coming from the North (onshore). It blows 2-3 days, 4-7 Bft. Strong in autumn and at spring time is quite often. The last 2-3 years was better in summer time as well 1-3 days/week with bigger kites.
You can come to Budapest with plane and travel to Siofok with car. It's 100 km trip on a motorway. Before you reach Siofok (2km) you should take the Sosto interchange and go down to the beach. You will see the kites in the air. The spot is on the south side of the lake.