I had it on a K1200S, used it quite a bit, and could definitely notice the difference between sport and comfort modes.
Despite it being good, it spent most if its time on the sport setting.
I did change the setting between solo and passenger, but that's only really a twist of pre-load.
I know of a few people who have had them fail and they are bloody expensive to replace (although most were done under warranty).
I don't have it on my GS, and don't miss it at all (especially since fitting a set of Wilbers shocks) - I can manage to turn the remote pre-load almost as easily as pressing a button on the handlebars.
TBH, if you want it and can afford it then why not?
It will probably make the bike more desirable when you sell it (maybe).
Just be aware that if they go wrong its really expensive!
The clincher for me would be if the actual ride feels as though the bike is better sprung than the non ESA version.
Adding fancy adjustment to a poor or too soft shock doesn't address the underlying issue - so if you think it needs to be sharper, then spend your money on aftermarket conventional springs rather than ESA.
Personally I wouldn't go for ESA again - it was cool at the time but, with hindsight, there were better things I could have spent the money on (like an exhaust system and PCIII).
