Electronic soil tester

I saw a Ferry Morse Electronic Soil Tester yesterday at HD, for $19. Has anyone used one of these gizmos, can you tell me how reliable it is?

I have one from Charlie's and it works pretty well, or so I suspect. When I put it in a cup of water mixed with lime it spikes to the alkaline side, so I trust it to a point.

I've also wondered how these work--anyone else have experience? I've been cynical up to now, but it sure would be handy not having to wait for soil analysis if you just want to plant something in a new spot, know the Ph etc.