Most DP type level transmitters use an 'O' ring seal which will perish within 6 to 12 months usage in a hostile process environment. The FCX series transmitter uses an all-welded construction with fill fluid that has been subjected to high vacuum for an extended period to remove entrained air. This provides long term reliability not found in any level transmitter of it's type.
Each application is different. Please feel free to get in touch to discuss your requirements.