I read about this in the June 16 edition of MacLife magazine. They gave it a pretty high rating and the functional idea was alluring. I got the free iPhone & Mac apps, did the install,and walked away from and near to my Mac with the iPhone in my hand. Sure enough, as l walked away the screen went black and when I sat down at my desk, poof! Like magic the Mac happily lit up and logged in before I could get the chair situated to my workstation. I thought this is cool! The $4 upgrade price to the Pro version (which is necessary to un/lock the Mac with the iPhone in the "off" mode) was reasonable, so I plunked down my moolah and was happily locking and unlocking with the dark iPhone in my pocket and the retuned to work. After about 20 minutes, my Mac logged out for about 10-15 seconds, and logged back in. "Fluke" I thought, and went back to work after a while it did it again. "Hmmm" I thought. Over the next 90 minutes or so, at irregular intervals it toggled another 4 times and I uninstalled the app. At the moment, l wish I had my $4 back.
It is a very cool idea, and may very well work for you, but I suggest you try the free version extensively before upgrading to the pro.
Addendum: heard back from support within a few hours of sending an email (impressive). They explained the environmental factors to consider that would affect not just Near Lock but any similar apps as well. Im giving this another chance. Pushed the threshold out to 6 and with my phone within 18" of the Mac Mini I have not had a repeat of the unclogging issue. Support also mentioned they plan on releasing an update in the near future that should improve reliability.