I have tried different sets from nickels and a set of Stainless Steels. The stainless steels are obviously a bit stiffer than the nickels but that's just because I was used to the feel of the nickels. I you compare them with any other set of SS, these are butter. The tone and growl you get out of these strings is just unbelievable. These ones actually do last a really long time and keeping their primary tone without going dead. You get to pick your own sets and you can even calculate tension from string to string and work your way from there. They are not that pricey, what makes them pricey it's buying them outside the U.S. The shipment costs, in my case were the same or even more expensive than the strings themselves.
Best strings I have tried. They last an EXTREMELY long time. Very flexible, but maintain tension (.124 Kalium has more tension than .135 D'Addario). Great growl. Plenty of zing when new(if you like that), but mellow out after a while and maintain this tone for a LONG time. I have been rotating the same few sets for two years with just taking them off and soaking them in denatured alcohol overnight. I play a set about a month and then rotate. After a soak, they sound like they are only a couple of days old again. This is after more than a year! The smaller strings are starting to show fret wear, but if you played fretless they would last until you broke one!