Good use of concept 2 Rower at gym??

Yeah, it sounds very good and should be very effective. You are getting a good amount of intensive cardio, which will be beneficial for fat loss and also for improving fitness levels, and you are also varying what you do, which is good for general overall fitness. It should definitely help reduce your body fat percentage as long as you are also eating a healthy balanced diet that is not overly high in calories. The weights should also help you with gaining muscle. It might be a good idea to add some strength exercises (such as push ups/squats/lunges/crunches etc) so that you get optimum overall body tone.