Have tested the Bikerzbits seat. You get a whole different sitting position, so was a bit awkward at first. Reason being, you sit closer to the gastank, so the steering gets unsteady more easily. I haven't measured how many inches, but the saddle is lower as well. Making your feet closer to the foot pegs, and your knees gets a sharper angle. Guess it would be great for persons of low height.
To get the seat fit the bike, there are 6 rubber knobs you need to take off underneath the original seat, and mount on the new one. I used the ignition-key to pop them back in.
I am a bit unsatisfied how it feels riding. But since I only use the Grom for small trips in town, I will keep the seat. Haven't tried it for longer trips yet, but feels kinda hard so might get your butt sore
Anyway, in my opinion it looks better than the original one so all in all I am pleased. Hopefully I will get used to the riding as well. Have only tried it for 20 minutes yet.