I use a Garmin eTrex 30 with open streetmaps and think its really good. No HRM but I don’t care about that. Use maps.bing.com (OS level 1:25000 zoom for free) to create routes, export into GPX, import into Garmin Basecamp and then send to device.
Colour screen a bit small but OK for following a purple line on a MTB.
Mounts are zip tied on, the genuine garmin mounts are good, the cheap £2 ebay ones don’t latch the GPS very tight and I’d have lost the GPS if it wasn’t saved by the lanyard.