I bought these specifically because they are small bullet style IEMs. They can sit a bit deeper and I've always found larger IEMs to fall out or lose seal too easily. These sit well (using the largest ear tips in my case) and maintain a good seal even when walking. comfort is also excellent, for me at least. I wear them with the cable over the ear and there are minimal cable noises even when walking around, also important to me.
The sound is good and I'm impressed by how solid the sound is given the tiny size of the earphones. I have made some minor EQ adjustments at source to lower mid-bass a bit and add a little more treble, this is entirely a matter of taste of course and not essential. There's a lot of bass available and EQ is small to be close to Harman curve if that's your thing. Some reviews suggest isolation isn't that good with these IEMs but I find them better than ANC TW IEMs because the fit/seal is so much better.
Having tried several IEMs and over-ear headphones I've concluded that comfort is one of the most important factors in selecting them and that is a very personal thing. I expect the E4000 (or the other E series for that matter) will work for a lot of people because they are very small.
While the E4000 is "harder" to drive because of low sensitivity my Sony xperia 5iii will go very loud without distortion. I normally use a Qudelix 5k BT amp and that works brilliantly with them, including the built in EQ functions.
The travel case is a bit bulky in my opinion but there's a useful tool for easy cable removal in the box which is great.
