I tried this and it did nothing for me. For a start, the white dots disappear on a white background, so not a good start. The main thing, though, is while it picked up on the vehicle turning it didn't pick up on acceleration much, which is what actually gives me motion sickness.
The biggest issue Android has both with Kinestop amd this app is unlike Apple's system it does not count for acceleration. I find myself having to look ahead when under acceleration or braking. I have experienced the Apple's motion cues when my friend got curious if it would work because he had no use for it since he did not have motion sickness and I'm unsure if it was just psychological but it felt better than Kinestop which I use.
When did you try it? I got a bit confused by your comment because there's no obvious reason why the accelerometers in an android phone would have a problem reporting forward/backward acceleration any less accurately than lateral. So I installed it and the 'Dots' mode definitely responds to acceleration normal to the screen, but that mode is marked as 'New' so might not have been present when you last looked.
It's supposed to handle acceleration though, if you bring your phone to your face quickly dots get larger. I've done some in-car testing, but things get squeamish quickly so it's not the easiest to validate.
Changing the color / adding some contrast would be quite a simple change