Here are my thoughts on the EP004K. It picks up golpes (unlike USTs). String-to-string volume / balance is not an issue. It does indeed require drilling. It does not affect the saddle/bridge connection / vibration transmission. It does not have the same level of quack/plastic sound that USTs are notorious for. You can use it to record in a noisy environment and the signal will be totally free of the ambient sound that you want to reject on the recording. It is very high-value (quite affordable for what you get).
At 3:39 in the video, I apply an IR to the signal.
