No worries, will give them a go, hopefully they last as long as Pressurewounds!
Speaking of Pressurewounds...
I tried the Rotosound Solo Bass 55 (stainless steel pressurewound) before trying the Ultramags. Surprising enough, the UMs (roundwound) actually felt smoother under my fingers than the SB55 (pressurewound). I guess that's the difference between stainless steel and Alloy 52.
The UMs on my Sandblasted J are only two and a half months old. I intend to keep them on there to find out how long they retain their useful tone.