Is it better than the free ones (ex. lisp by sleepy time) or more comparable to the Waves $29. Or maybe a more higher end one like SPL? 

I think it does a pretty good job. I've used it on a couple songs, and it performed exactly as I wanted it to on both occasions.

Leadfoot
I think it does a pretty good job. I've used it on a couple songs, and it performed exactly as I wanted it to on both occasions.

Very interesting. I had the opposite experience. I couldn't hear any effect. Even when I switched to the mode where you hear what it is removing, I could hear nothing.  I wish it would work, because I like VX-64 for the other things it can do. I had to switch to the de-esser in Ozone Nectar Elements.

Sometimes in Splat, you might try toggling on and off the pre/post switch on the audio channel. This has been a bug for a while that reoccurs from time to time. I also have had good results with the de-esser.

I often use it in conjunction with other de-essers

I use Vx and percussion 64 all the time. They work great for vocal and drum tracks, but the Deesser doesn't seem to do anything, at least as far as these high decibel earphone ears can discern.

a6strng
Is it better than the free ones (ex. lisp by sleepy time) or more comparable to the Waves $29. Or maybe a more higher end one like SPL? 

It is usable, but not great.
 
I typically will use a few stacked in layers if I'm doing a super vocal-centric track.
 
A decent cheap one is HorNet's pro version.  (currently less than $14 USD)  You can "listen" to each filter and then apply and adjust each band.  
 
Check out the Blues Tubes on in your Platinum package.  Also usable, and works stacked with a few instances of it each set differently.  
 
 

 

Bristol_Jonesey
I often use it in conjunction with other de-essers

I do the same thing and its works very well. Stacking the de-essers

Check ToneBoosters Sibilance.

If you want the best results possible, use one band of a multiband compressor.  This will give you way more tweakability.  Center the frequency at the troublesome pitch of the sibilance.  You can adjust the Q, attack, release, ratio, etc. and get far better results than even the best de-esser plug-in.
 
Ultimately, this is how a de-esser works, just with less control.