The E4 is one of those toys which, on paper, looks as though it has everything going for it; it's made by Jopen, it's silicone, it's waterproof, and it's rechargeable. It turns out, however, that there's a very sharp divide between where it succeeds in form and fails in function.

The design of the E4 is by far my favourite feature of it. It's actually a surprisingly small toy when you first look at it, measuring only 3" along one side and 4 1/2" down the other, and it nestles into the palm of your hand. It forms the shape of an upside-down number seven with two bulged ends, and it slots neatly between the right-angled L-shape designs of some manufacturers, and the horseshoe-like C-shapes used by Rocks Off. The whole toy feels very solid and rigid, but it is coated with an outer layer of royal blue silicone, which gives the surface a little give. The finish is generally good, aside from a subtle mould-line which can barely be felt, and the silicone has a soft velvety matte finish.

The circumference of the insertable portion is 4 1/2" around the widest point, and it slips quite easily into the body. It should be suitable for the majority of people, though your complete novice will likely require a little warm up first. Once it's inside the body it feels very comfortable and it sits in the perfect position. The short arm of the E4 lies flush against the perineum and applies a nice gentle amount of pressure, while the long arm does the same for the prostate inside the body. I actually couldn't like the shape more, in terms of wearable prostate massager designs this shape has to be my favourite because it actually works with my anatomy. The other great thing about the shape is that once it's inside the body it stays put, with absolutely no slippage, so you can wear it whilst walking around or while having sex, and it won't be going anywhere. The shape also allows for you to comfortably use the E4 in the seated position if desired. As it's not the biggest device it's naturally not going to feel that filling, but as someone who generally does prefer big toys I have to say that this actually wasn't an issue for me, and it just felt like wearing a really pleasant butt plug.

The vibration for the E4 is created by the PowerBullet which is located in the perineum arm of the toy, much like in the Lux LX-3. I for one will never understand the logic behind this, and frankly I find it incredibly irksome. These products are intended to be prostate massagers, therefore you want the vibrations to be primarily applied directly to the prostate, and that means putting the motor in the insertable portion and not outside of the body. When you turn the E4 on it starts off with a very gentle and low rumbling vibration, which seems like it would be quite pleasant as a first power setting just to warm you up. When you press the button for a second time the E4 turns off again, which originally made me think it only had one power level. To increase the power you need to hold down the button until you reach your desired strength. The vibrations seem to do a reasonable job at travelling down the rigid body of the E4, and initially they feel around 80% in the insertable portion the strength of what they do at the source. As soon as you hold the E4 directly by the end with the motor you'll notice that the strength of the vibrations at the opposite end drops down to only about 50%, and this presents a slight issue during use.

When the E4 is being worn inside the body the vibrations feel quite pleasant at the highest power, but they're not really that special. There's a soothing tingle along the perineum, but inside the body there's not that much of note to be felt. There's no real 'oomph' going on, as the vibrations around the insertable portion aren't strong enough to draw your attention to your prostate, let alone penetrate it deeply and create pleasure. The positioning of the motor really spoils the E4 and makes it one of the more lacklustre products I've used. It delivers slightly more sensation internally than something by Rocks Off, or your basic vibrating butt plug, but overall it is rather a disappointment. Even if the motor was in the correct position and could deliver the power where it was needed, the fact that it has no vibration patterns lets it down equally. Constant vibration in my prostate does little for me, it's rhythmic pulses which really deliver satisfaction.

If there is one thing to say about the motor in the Ego E4 it's that it's quiet, and whisper quiet at that. At the lower power levels you could stand silently in an elevator with it turned on and the person next to you would be clueless.

The E4 is charged by USB which reduces the bulkiness of the cable, which is handy if you want to take it travelling. If like me you're not a huge fan of having to plug every gadget into the computer to charge it then you can buy adaptors which allow you you plug the cable into a standard power socket in the wall. A blue light on the power button illuminates when it's charging, then goes out once the battery is full. The initial charges takes just under 3 hours.

The Ego line all comes in some rather nice packaging. It's just a simple cardboard box which slides open to reveal a solid foam insert with recesses cut into it to house the E4 and cable. Altogether it's not that bulky, so it's useful for long term storage.

To care for the Ego E4 you want to remember to only use a water-based lubricant, as it may react with silicone. To wash it after use you can simply use anti-bacterial soap and hot water, and the toy is safe to submerge. Alternatively you can use a spray on toy cleaner or a toy wipe. To sterilise the silicone you can wipe it over with a 10% bleach solution, but don't attempt to boil it as the heat may damage the electronics.