Note that for most of us, the non-TLER firmware is probably best, even for RAID applications -- the non-TLER firmware will give the most reliable error-protection for our data.

[EDIT]
There should be no real performance difference between TLER and non-TLER except when handling media errors (but see my subsequent post below).
[/EDIT]

The folks who need TLER are companies like VISA, who don't appreciate it when their entire transaction processing system comes to a halt for for 10-20 seconds just because one drive in the array has a bad sector..