I went to Toyota motors today to check the same thing and yes they have it here in PK corollas, probably due to wide weather patterns in Pak, however it should make a little difference both in economy and performance according to them aswell.
according to different user accounts elsewhere though, the difference is .5 to 1 km/lit in economy, power cannot be measured but they all report a smoother ride.
Its recommended for sub zero conditions, and can be reversed may be in 5 minutes.
hope it answers ur questions, i am planning to get it done in a few weeks(moving to Karachi)
ps check out the Singapore, Bangladesh or westindian axio forums they all have it done