Reasonable level of inaccuracy in thermometer?
That is ridiculous. 5% is simply too large for an acceptable margin of error. I'll accept 2 degrees F tops, and I have never spent that much on a thermometer. 

If you want to spend that kind of money, this one won America's Test Kitchen testing:



That's the Thermopen. It's accurate to less than a degree F and it gives a reading in 3 seconds.

These two thermometers tied the testing for less expensive thermometers. They are both also accurate to less than a degree F.

RT600C Super-fast Water-resistant Digital Pocket Thermometer

CDN DTQ450X ProAccurate Quick-Read Thermometer

Incidentally, this is my scale. Amazon tells me that I bought it in July of 2011. I highly recommend it, it's spookily accurate. That scale, a dollar store timer and one of the recommended lower cost thermometers would pretty much wipe the floor with your product at significantly less than half the price, and would be more convenient to use. I want a timer I can put in my pocket, and a thermometer I can bring to something on my oven shelf without bringing my scale along for the ride.



To me, that makes no sense, imagine trying to gauge the doneness of a Thanksgiving turkey with that thing! Never mind that you can't trust the reading.