I put S3004's in my NexStar, and it works fine. The difference between the 3003 and 3004 is the 3004 is a ball bearing servo. If you look on tower at the specs, all the specs are the same. I always be with ball bearing where ever possible, but that's just me. If you haven't flown the NexStar yet, you'll love it! It's a really great flying plane!