What's the best way to clean the injectors then?
Take them off the car, check flow rate and pattern, ultrasonic cleaning bath then check flow rate and pattern again. This way you know they are performing to spec, and know if you've made any difference. Any that don't perform afterwards you can replace.
Squirting fluid in on the engine as with Terraclean is only going to clean the injectors anyway, as a modern engine won't accumulate any significant carbon deposits, as said, and the fluid doesn't go anywhere other than the fuel rail and injectors, so it can't clean anything else.
For the cost of a Terraclean you can get a set of injectors cleaned
properly and have change for a night out. No brainer. Not that injectors get that badly clogged unless they've sat in a breaker's yard for years, IME.