FWIW, I have other (non-aviation) weather apps on my phone that include similar arrows, but in my experience when you watch the radar loop and compare where the weather actually went vs. where the arrows said the weather was going, the arrows are very often wrong.
That said, I don't know where the arrows come from, so I don't know if different apps might show different arrows and maybe some apps could have better arrows than others.
At any rate, I've learned/been trained not to give much credence to those arrows in the non-aviation wx app I most frequently use. I would prefer not to have stuff like that in iFly if it's not reliable. Like Mike, I find the radar loop function to give me the info I need to make educated guesses about how things are developing.