I recently found the Hansgrohe Raindance E 120 AIR 3-Jet selling for $59.97 at Costco and decided to give it a try. I also have a Grohe Relaxa Plus and a Hansgrohe Interaktiv 2-Jet Handshower installed. When I purchased the Raindance, I thought I could just switch the handshower units. However, the the Raindance operates a bit different from the Relaxa Plus and the Interaktiv handshowers. Unlike the Relaxa Plus and the Interaktiv handshower units, the Raindance handshower has the flow restrictor built into the showerarm mount (where you hang the handshower) instead of into the handshower unit itself. So, if I just swapped the handshower units, the Raindance would output more than the reported 2.5 GPM maximum flow rate.
Out of curiousity, I had a 2.5 gallon plastic bucket in the laundry room. First, I filled the bucket using the Raindance handshower. The bucket started to overflow at around the 50-55 second mark, which is close to a 3 GPM mark. Next, I filled the bucket with the Grohe Relaxa Plus handshower. Despite the same reported maximum flow rate, the Relaxa Plus needed 1:40 minutes to fill the same bucket, or about 1.50 GPM. I always assumed that my showerheads were outputting at the maximum flow rate. Get a bucket and test your showerheads and see if they are delivery more or less water than the reported maximum flow rate.