The black component in the photo is indeed the pressure reducer, and at least with the municipal water pressures we’ve tested with it should lower the force of the water stream enough even for smaller plants.
It is possible though that your incoming water pressure is much higher than what we’ve tested with and so even with the reducer it is still too powerful. Perhaps a quick hack is to add a zip tie (or a few) to the water line going from the pressure reducer to the tool head. Slowly tighten the zip ties to restrict water flow until desired.
If you’ve set up any sequences yet to water based on time, you’ll need to make adjustments for this reduced flow rate.