I have used E604s on countless gigs for years, but never actually owned any.
They are super easy to clip on and are fairly small and will not get in the way of things in a live situation. I have used them a lot for recordings with great result. comparing cost and sound quality it is hard to beat. Will keep using these for many more years to come.
Sound-wise they are nice and clear on the toms, with plenty "meat" on the lower frequencies ,in my case 14" and 16" floor toms. (For the one on my 10" tom I boost it a bit on the highs, and my 12" and 13" toms I keep the high boost and add a little on the mids, and the 14" +16" get the low end boost as well a bit of compression.
They are also very useful as a snare-side mic, and as vocal mic for drummers (very small mic and can be put on a mic stand behind you)
Pros: sound quality, durability and cost.
Cons: would be great if you could use angled xlrs, but for that to work the mic would have to be set at the very top of the clip, whereas the best result(in my opinion) is achieved when having the mic closer to the drumhead.