The main reason is that they place an excessive amount of shear force on the knee. TPS will never, ever have one. Period.
|Never use this, it might fall over on you and cripple you.|
I have found a new reason to hate them. In today's Boston Herald there was an article about Cybex losing a $66 Million judgement in an injury suit regarding a leg extension.
It seems that some poor person had a leg extension FALL on her and it crippled her. Just one more reason to avoid the leg extension.