I'm an avid runner and log many miles per week.  I'm also very technically saavy but not necessarily an early adopter of the newest thing.  Finally, I've had this watch for a while and have some long-term observations.

SHORT VERSION:  This watch is a great deal for the cost, and much easier to deal with than fussy, expensive GPS watches.  If you are a RUNNER, buy one, you won't regret it. If you WALK, buy a pedometer, this watch won't work for you as it counts exaggerated arm motions of the type while running.

LONGER VERSION:  I've tried at least 3 different GPS based watches over the past several years and returned them all within a few weeks.  To me, they're a complete joke.  Their biggest problem, as I see it, is they don't track properly when you run under or near any obstacles like trees, of which there are plenty here in Michigan.  Add to that cost and complexity issues and they're just a bad idea as far as I'm concerned.  My life is complicated enough that I don't want to load "firmware updates" to my watch via USB.  Who wants to wait for sometimes several minutes while your watch finds satellites before you can start running?  Not me.

By the way, you can throw smartphone apps in the same category - how can you concentrate and enjoy your running if you're constantly fussing with some phone and worrying about battery life, music selection, voice prompts, etc.  Just annoying. This technology thing is getting out of control.

Prior to purchasing this watch I would go for a run with a digital Timex watch that had a stopwatch, time my run, come home and map the run using Mapmyrun.com and do the math.  Very simple, accurate and reliable.

Enter the Casio watch.  Sometimes I want to run on trails or want to keep track of how far I am during a run.  This thing is simple as can be:  figure out your stride length, enter in watch, go running.  Sure, it's a little more complicated than that but not a very steep learning curve. When I come home, it tells me my overall time, lap times (if I pressed the lap button, more on that later), my average number of strides per minute (very useful if you follow the Chi-running or barefoot techniques), calories burned.

To figure your stride length, run a known distance (like a mile or half-mile) while counting the number of steps, do the division and figure out your stride in inches, enter in watch.  If that's not enough explanation for you then don't buy this thing or anything complicated for that matter.

MY ONLY COMPLAINT:  Amazingly, the watch doesn't have an auto-lap function which is the only reason why I can't give it five stars.  I'd love to have it record my time for each mile as I complete it.  The only way to accomplish this is to press the lap button while staring at the display.  As soon as it clicks to "1.0 miles" or whatever, press lap button.  Trouble is, if you stare at the watch and stop moving your arm it no longer counts strides so you'll be staring at the watch and throwing off the accuracy!  It's such a simple software issue to build this functionality into the watch that I have to wonder if it was not designed by Casio engineers who actually run!  Come on Casio, are you listening????  However, the unit does have the capability to end your workout when a certain distance or time have been completed.  So I suppose you could set this to 1.0 miles, then start another "workout" every time the previous one ends.  But that's too much distraction for me and then you're stuck adding up all the mile times in the end.  No thanks.

ACCURACY:  If you measure your stride length correctly this unit will be surprisingly accurate.  However, you can only enter your stride to the nearest inch when perhaps the nearest half-inch would be better.  Also, if you're recovering from injury or just going out for a leisurely recovery run (and consequently shorten your stride) then take an inch or two off your previous measurement if you want to be real precise.  But I'm picking nits here - even if you don't adjust the measurement this watch will still be pretty close.  For instance, it's always within .1 miles on a 5+ mile run.  Close enough for me.  Use mapmyrun.com if you want more accuracy.

Finally, let me say that I had to send in one of these to Casio repair after it stopped functioning properly.  They fixed it free and I had it back in less than a week.  Nothing to complain about there, and it's been fine ever since.  Even if I had to throw out the old one and buy new it's still a cheaper route and GPS watches.