I'm really interested in the K1, but every review I've read says it's slow as molasses. Are they exaggerating or does it really feel bad to use?
In what sense? I haven't tried anything CPU-intensive on it, since there isn't much point with that kind of screen.
If you mean the screen refresh rate, it's typical eInk, comparable to Kindle. For tasks that require fast refresh, it's certainly not a pleasant device to use - e.g. scrolling around in maps is a bit tricky - but it's manageable.
With K1, I have a 400 Gb card in there that's loaded with stuff - not only my entire Kindle library, but also Kiwix loaded with offline Wikipedia and a bunch of other wikis, OsmAnd topo maps etc. Between that, and several days of battery life with occasional use, it's perfect for multi-day hikes out in the boonies.