I feel strongly both ways (as my friend Ralph Schuckett was fond of ambivalently saying)
on the one hand, Steve Massey makes great plug-ins that are VERY reasonably priced.
So why wouldn't you?
on the other hand, I feel that de-essing is one of those things that tends to be way overdone, mostly I believe because people convince themselves that's what you "need to do" to have a "professional" vocal, rather than it being really necessary.
add to that that better recording techniques (like no stocking hoops, no over compression, singing in a direct line with a good mic...) are the way to correct sibilant problems before they occur.
so, my bottom line is that I find I need a de-esser (REALLY need one) once in a blue moon, but not regularly.
and in those instances, I find the free Digi de-esser works just fine.
but I'll bet this Massey plug-in works great just the same.
see?
both ways.