Hopefully you type fast enough that by the time your brain noticed any lag on the "j", you are already a few letters down the line.

If you are too dependent on visual feedback while typing, you'll have a difficult time typing fast in any environment.

That said, I don't think I'd ever try remapping escape. I have long fingers though.

It's just an ugly way to do a mapping. I used to have some mappings like these in my rc, but I removed them in favor of similar ones that backtrack instead. If the author wants "jj" to be <ESC>, it can be done without the lag: You just check the previous character on 'j' and then take action accordingly.

Can you show us the script you use to make this happen? Sounds interesting.