Agreed with Osmand - I used it for ages until I first got a Garmin, it's so good but battery life on the phone with the screen on made it impractical once rides were of a significant length.
Thinking about it, wonder if you can run Osmand on a Hammerhead?
Cc @passhunting
How long are your rides?
I'd use a phone app. Great screen and clear OSM is a winner. Plus you have one already.
Lots of apps for free, ie. OSMand, Maps.me that you can upload a gpx into. Tbh you could even use Google maps.
Tbh it sounds like a dedicated device is the opposite of what you need or want.