I suppose it all depends on how much information and how many features you would like. I had a vear or two using nothing more than a wireless cycle computer and pre-written course cards for unfamiliar routes.
I now use a Garmin Edge 200 which I am getting along with really well. In addition to the basic current speed, distance and average speed that any cycle computer will provide, I can devise a course on pc using ride with gps, map my ride etc. then drop it onto the 200 as a course to follow, which I find works really well. It's not a map, only a breadcrumb trail, but if I miss a turn an alarm sounds and the display advises how far off the course is and which direction to get back. Not that I've used it yet, but if you need to bail mid ride there's a 'get back home' option too.
You don't get cadence or heart rate monitoring, but you do get a small, light, easy to use directional aid for an 'accessible' price, with really good battery life. Uploading rides is easy too, along with all that checking how you are doing compared to other riders business on Strada.
I'm entirely happy with mine.