I used https://github.com/deoxxa/hl7 at my last job to grab HL7 messages out of central processing system.

Regardless of the parser, I agree. Writing your own is dangerous. HL7 is deceptively complex. It leaves a lot of room for vendors and your hospital to customize. If you write your own, you can very easily end up with a system that is boxed in to your hospital's own, or even your department's own, implementation.