Yes - although the Peplink appliances are SDWAN Appliances first. Their firewall capabilities although very successful, secure and reliable, are not a like for like replacement of a SRX. You should compare them and make sure you can do everything you want with the Balance.
All of this is fine.
Test and test and test again. No one here can know exactly how your network works or is configured - only you do.
Generally if I want to test a Peplink install beside an existing one I install the Peplink beside the existing router. See the tech documentation for the Pluss deployment. IN particular the deep dive for a real world migration example.