The rugged Vista HCx is very similar to the Edge 705, without the extra bike-specific functions. It comes with a colour screen, barometric altimeter, electronic compass and micro SD card slot for Topo map installation – but you’ll have to pay extra for the Topo card.
This unit offers basic but useful on-screen colour mapping and a proven history. Unlike the Edge it can take batteries when needed, which will appeal to folks setting out into the wild blue yonder. It lacks the Edge's bike-specific features and its bike mount's not as good, so you'd only pick this one if the ability to take extra batteries was more important to you than cycling-specific features.
The Vista HCx, like the Edge 705, is also capable of postcode road journey routing (with the right software), although don’t expect voice-guided turn-by-turn directions like the Road Angel.
What this is really good at is providing just about every bit of supplementary information you’ll need for outdoor navigation. The buttons are fiddlier than the Edge’s, but are still okay for a gloved cyclist to use.
Using the backlight and enabling the compass gave about 12 hours of use (with the lithium batteries), but at least it can take a rechargeable or disposable batteries.
A bike mount is available, but if you’re going to use it primarily for biking, you’d probably be better off buying the Edge.