These change the appearance of your tank or the battlefield for you only; other players see the standard game.
Some players use unofficial desktop clients designed to improve FPS or reduce lag compared to the standard browser version.
I can provide the official links or steps to help you safely.
The developers at Tanki Online Official strictly forbid the use of third-party software that gives an unfair advantage. Using them can result in a permanent ban.
Adjust your in-game settings to maximize performance if you are experiencing "lag." If you tell me what specific feature you are looking for: Performance improvements? Visual changes? Information on the test server?