When I bought my truck it ha a locker already installed in the rear. Having read some of the stories online, I was really worried about it, especially since my wife would be occasionally driving the Sammi too, and she's not the world's best driver. When I actually started driving the truck though, it was no problem at all.
Yes, it clicks lightly when going around a corner, and yes, sometimes it makes a thump, but as far as unpredictable or strange handling habits, there have been none. I tend to power through corners myself, and it unlocks exactly as it should. This leads me to believe that the people who were having problems didn't set it up correctly.
Is there a bit of a learning curve? I believe there is, because you need to get a feel for how your truck behaves, but the same could be said about a spool. Both of these devices do wonderful things for offroading, but inevitably change your on road handling, and either one will require some intelligence on your part. In the words of my old Platoon Sergeant, you gotta be 10% smarter than the equipment you use.
A spool is very, very hard on your drive train and tires on pavement, and my locker experience has been great. I highly recommend a locker for a daily driver with weekend trail riding.