It's good as long as you're careful. If the chain becomes too loose over time, you might be facing chain getting wrapped around and jamming the drive sprocket on the motor. Also, I would think that you'd need your rear sprocket and the motor sprocket to be in good-enough alignment for this to work long-term. But I haven't heard of anybody without a tensioner have any problems. Just be careful, I guess.
Why, may I ask, did you remove the master link?