You are good. The plastic versions don't have the strength of the brass type.
As long as the brass or copper is before the RO it does not matter since the RO/DI removes all traces of copper. It's after a membrane you don't waant to use any brass or copper since RO and RO/DI water are very agressive, trying to get back to their natural "dirty" state so they attract anything they can to replace the ions that have been stripped out.
Mine has been hooked up the same way for about 13 years now and zero issues.