I bought the Off with Their Head Cap as I was intrigued by the idea of having a silicone cap for my Hitachi for sanitary reasons and many reviewers raved about the ridges as enhancing the Hitachi experience.

Look/Feel:
The attachment is thick, high quality silicone. As others have mentioned it's definitely a draggy/tacky sort of silicone and not the kind of silicone found in other sex toys I own which glides more smoothly along your skin.

Ease of Attachment:
While it was difficult to get the original Hitachi head off, getting the Off With Their Head attachment on was easy peasy. I have no complaints (except what a bitch it is to reattach the Hitachi head).

Cleaning:
As it comes on and off easily, cleaning is simple and similar to your normal silicone toys. You can bring it to the sink and wash with soap/water, toy cleaner. One of the big plusses of silicone is that it is fully sanitizable and if you are sharing you should sanitize in boiling water or the top rack of the dishwasher.

Experience:
At first I was just thrilled to have a new toy and used the Hitachi with the Off with Their Head Attachment regularly. I had also bought another vibrator at the time though and ended up favoring the other vibrator to my Hitachi Magic Wand. After a couple of weeks, I decided to give the original head a try again and realized that the Off With Their Head Attachment had been dulling the sensations of the Hitachi. Ever since I removed the silicone cap, the Hitachi has become my favored toy.

As another reviewer had mentioned, there is a lot of fuss made about the ridges. I would agree that the ridges really didn't do anything special. I didn't feel they necessarily conducted the vibrations any better and for me it really wasn't very exciting.