The Double Whammy is a double sided cock ring with a removable bullet vibrator on each side. The ring stretches to fit around the shaft of a penis, and the vibrators are meant to stimulate the vaginal area both above and below the vaginal opening. It can be used with both penis or dildo/harness, solo or couple play, etc. It's versatile in its use, which is good.
Now that I've been through the technical stuff!
This ring has a good concept, hands-free stimulation as easy as slipping on the ring and going at it as usual. Unfortunately the concept doesn't fully pull through as intended, but I'll get to that later. The bullets do come out, and use watch batteries.

The texture of the ring is TPR Silicone, which is a stretchy, soft, and a little sticky. This makes it a little difficult to clean, especially since stuff sticks to it so easy, and it has the ridges. Speaking of which, the texturing is thin, soft tendrils. They're not super noticeable-- to me anyway-- but if you're sensitive to textures, they'll probably be nice.

The bullets are removable, and come out pretty easily. The downside of the removable-ness is that when you're pressing the buttons to turn them on, they tend to slip out of their stretchy little tubes. They are pretty easy to remove, though, which is good.
It claims to fit all sizes, but my boy, who is average sized in thickness, wasn't particularly comfortable in it. Granted, he doesn't use C-rings often, and it's not like they're meant to be comfy to being with. But he was definitely glad to have it off.
The biggest problem I found was that the bullets are right against the ring itself. This means that it definitely makes the shaft vibrate (which is neat) but doesn't get anywhere near the clitoris, which is what is really preferable for hands-free stimulation! It really needs some kind of segment for the top bullet that pushes it away from the shaft and towards the clit!

The bullets that come in the ring are basic bullets; one power button on each, one vibration setting. Nothing special, but they're pretty powerful. I didn't have too much luck with the ring itself, so I pulled one of the bullets out and used it alone. It was pretty effective that way.

Cleaning is a little bit of trouble, since the TPR Silicone is a sticky sort of material, but a good spritz and some careful time getting in between the tendrils.
As mentioned, the batteries are basic watch batteries; easy to replace.
It doesn't have it's own storage area, since it comes in a simple cardboard display case, so it kind of needs its own area in your toy box, but no trouble other than that.

The Double Whammy is good for someone looking for hands-free stimulation during intercourse or solo play with an insertable toy.
Personally, I didn't have very much luck with this product because I require full clitoral stimulation for orgasm, and no matter how much we tried to position ourselves, it was virtually impossible to get the bullets to sit anywhere near that high up. This is a problem which might be fixed during solo play by using a dildo and positioning it just right, but probably only if the dildo can bend...
It's certainly an interesting feeling, being buzzed on the inside, and for most would probably be quite pleasant, but for me the ring and its parts just didn't live up to their purpose. I always ended up taking out one of the bullets and using it by itself (worked very well).