Yeah, should be decent. I've installed rain shower with no pump heater for my friends, everything is fine, but they have good water pressure in their house and shower head is not big.
But if I were you, I'd save money for a better heater. IMO, small rain shower heads doesn't provide the same quality as bigger ones.

1. Guide is here. Normal water pressure is typically between 30 and 80 PSI.

2. The size of a shower head can affect pressure. Larger sizes obviously deliver a larger area of “rain” for your shower, but if you have bad water pressure, a larger size with more nozzles will make the problem worse. When the water pressure is low, the “rain” shower ends up an unsatisfying drizzle. Smaller showerheads with fewer nozzles will have more pressure. But IMO it feels like a regular shower. So you''ll need to check water pressure first. Since my wife asked me to install rain shower for her, I've tried several options before I choose ours. We have 50 PSI (city water) and we're using an average sized showerhead, it feels good. IDK, maybe you'll find something helpful in reviews.
http://www.visionarybaths.com/blog/2016/05...al-shower-heads
https://www.businessinsider.com/best-shower-head
https://wisepick.org/best-rain-showerhead/
https://www.bloomberg.com/news/articles/201...nd-eco-friendly

Feel free to ask me anything if you need