I used them for a couple years
I put these on a Schecter 006 Elite with stock Duncan Designed pickups. I have used DR MT-10s for about 20-25 years but on my Schecter they sounded a little smeared on the G, B, and high E strings. After reading about the Cobalts in a guitar magazine I decided to pick up a set.
The positives of these strings are that they are slightly louder and a little brighter than nickel wound strings, such as the DR MT-10s, and have noticeably more definition on the G, B, and high E strings. They stay in tune well and tune right up.
The downsides are that they have a stiffer feel, are a little more difficult to bend, and due to the hardness of the metal will chew up your picks (plectrums?). Also, instead of losing their liveliness gradually, they kind of hit a wall and lose life very quickly.
My verdict is that for a guitar with pickups that aren't that great, or on a dark sounding guitar, these will improve your sound, especially if you want some more definition than the standard nickel wound strings provide. If you prefer easy bending and a more predictable loss of string life, I'd suggest not using the cobalts.