ER tech experience good for ICU nurse???

It depends on the level of the ER. If it is a major trauma (knife & gun club) facility, the experience would undoubtedly be beneficial. However, if it is a low level "clinic" type facility - not so much. But in the long run, any real experience is better than none. The real advantage may be the opportunity to participate in training courses offered to employees, becoming familiar with the electronic charting system, understanding how different clinical departments work together, how various diagnostic tests are performed, etc. All of this will give you a real leg up when it comes to your first job.