As a temporary setup for very young engineer gobies a nano can work, but 7 gallons is too small for a permanent arrangement. Smaller individuals can be a rather difficult fish to feed unless they are the only thing in the tank, so a nano can make feeding a lot easier. Small engineer gobies have high food needs; unless there is a huge pod supply, feeding has to be 2-3 times per day with young fish, and smaller tanks do make the feeding easier. However, any engineer goby raised in a small tank will need a bigger one eventually (and the feeding becomes easier with larger individuals). The one I have in my nano will need to be moved to an upgraded setup as it grows.