Looking to buy a workout tower/powerstation for doing pull ups and knee raises

[Deek]

Hi

Im looking to buy a workout tower for getting a bit more toned and i am not sure which one i should buy as i dont want get buy one that moves around alot or bends when i use it.

Also

Please can you tell me if knee raises or leg lifts on this peice of equipment would help tone the lower part of my stomach.

See link for the type of equipment i am talking about



Thanks

Deeks