Butchering routes: I've had a points reduction feature put surprisingly large gaps between points, putting the track far enough from the road or path being followed that it's hard to see where you're supposed to go. I'm trying to remember if it's worse on sections of route which have been manually generated, rather than auto-routed.
It's not a serious problem, though. The other things I mentioned are more important, IMO.
I've not found an autorouting facility which is at all useful for bikes. This may be partly due to map data (e.g. not recognising that roads which are blocked off part-way to stop them being used as rat runs are usually excellent cycle routes, with a bicycle cut-through), but some of it must be down to algorithms. I think what's really needed is something that gives preference to minor rather than major roads (i.e. the reverse of the standard auto-routing), & recognises cycle paths (where mapped) as routes, & selects them when they're going the right way, not some manic "must find a cycle path & ride it, even if I have to do more on roads just to get to it than going direct" algorithm. I've got a beautiful example of this in Bike Route Toaster, which insists on doubling back along a road, going round a roundabout, & taking a couple of hundred metres of bike path under a road bridge - to get to a point 50 metres further along the same road from where the route had reached before the final click.
It's on Thames Side Promenade, Reading. And if I tell it to cross the river & go up St Peter's Avenue, it wants to go through the churchyard, which is most definitely not a cycle path. There's a no cycling sign at the entrance.
Those two examples illustrate both algorithm & map data faults, I think. The algorithm should be fixable, but I'm resigned to having to switch off auto-routing for plotting some sections.
One good thing, though: although displayed on Google Maps, it's got better map data in at least one place. It knows that one stretch of the Kennetside cycle path doesn't follow the straight line shown on Google Maps, but meanders a bit. Looks odd, the route straying off the path shown on the map, but it's because the displayed map is wrong.
I can't remember which one it was I've had a problem with doubling back on, I'm afraid. I do remember it wasn't all doubling back, just sometimes, & I couldn't work out what the difference was between the sections where it just did it, & the section where it was freaking out.