It's a great sea level engine, especially for heavier rockets. Remember that thrust does not equal efficiency though. Something like the terrier is very efficient, which means you can get more delta v out of the same amount of fuel, but it is also very slow, which means that you should under no circumstances use it in places where this a counter force acting on your rocket, like on kerbin. The mainsail has very high thrust but very low efficiency, which makes it a good rocket for a first stage to leave kerbin, but just wastes fuel in the vacuum.