Yeah electric units are easier to seal. Hermetically sealed means the compressor housing is welded shut, rendering all internal parts non serviceable but virtually eliminating leaks. I've seen leaks from a bad weld, major rust, or overheating that damaged the seals on the electrical terminals, but those are outliers. Here's a little one from a commercial under counter fridge, chopped open to show the internals. Bonus: can you spot why it stopped working?
Semi-hermetic units have internal parts including the electric motor in a housing bolted together with gaskets. Noisier, maybe less efficient at small sizes, but can be torn down for servicing instead of replacing outright for any internal failure. Common on older equipment and large capacity new equipment. Can even do fun stuff like variable capacity by shutting down banks of cylinders so one big compressor can act like two or three smaller ones. Here's a 6 cylinder 35 HP unit from a "small" brewery chiller. Can see the removable cylinder heads, reconfigurable intake port on the front, and variable capacity solenoid up top.
