Great for performance on full/near full drives, could be bad for drive lifetime.
I bought one for my wife's laptop which I purchased back in 2007. The HDD is starting to get loud and clunky so this and a new battery should extend the laptop's lifetime 3-4 more years. I plan to transplant the drive to the new laptop in future (though by that time, SDDs may very well be almost standard). With how little the laptop really writes, I'd expect this drive to last us many years.
I may even drop in a used T8100 depending on performance to replace the T2135...