I've never owned or felt the need for a deesser. They always struck me as fix it's for cheap mics or the wrong mic./room choice. It's rare that dynamics give you too much sibilance so use those if it's a problem. Some rooms and reverb patches will also greatly enhance unwanted sibilance. Deaden the room and roll the highs off the vocal reverb return.
They could be handy for rescue operations but if you are doing the tracking then just try to fix the problem at the source.