I received this for free with my order, it comes with a battery, and the strength of the vibration is actually quite strong. But getting it open can be a bit fiddly. Remember to take the battery out when not using it.
It adds the perfect vibration to a onahole. Just one tip: Definetly remove the batteries when not in use. The only thing that I found a bit bad about this was that I needed an insane amount of strength to open up the battery compartment.
For a free small vibe its pretty good, just take the battery out after using it, and for anal use only put in onaholes as your own is not a good idea as there is no base. As they say in the sex toy review/recommend lists "No base, without a trace"