Just tried playing on my desktop and didn't run into the speeding up/down issue so I think it was just my computer lagging.
Ah yeah, I saw the blue bar but, I would make it a bit bigger though. It's kind of hard to see while you're moving. Didn't realize the trails were only appearing when I was in the sun. That made a lot of sense though once I realised! Maybe you just have to tutorialize it somewhere or you could try making the transition between the effect turning off and on a bit more pronounced. I like the trail as an indicator though!