I think the biggest thing with Brown's speed and skating, is that he'll go into phases where he just doesn't move his feet. Not only makes him look slow, but makes him actually play slow.
Has some sluggish acceleration that could use some work to begin with, but definitely exacerbates it when he stops moving his feet. Starts just leaning on guys, rather than using the size+speed to power through guys (which he can do when he's on). Still works darn well in Juniors when you're six and half feet tall and have 40+ lbs on a lot of defenders. But it's my biggest concern with Logan Brown. That he sometimes slumps into kind of "lazy", low-tempo hockey - which makes him look like a worse skater than he really is.
Once he actually gets rolling though and keeps his feet moving, he covers a lot of ground quickly. It's the part of Brown's game that really reminds me a lot of Rick Nash. Where he's had stretches of disinterested play where he doesn't really look like a great skater at all. But when he's on and raises the pace of his whole game...he can really get moving and becomes extremely difficult to handle. I think Brown can be the same way, and does have that freight train speed/momentum when he decides to use it.