I've had similar experiences. You spend hundreds of dollars in hopes of getting settings you just KNOW are accurate and find out the product drifts.
I had an i1 D2 meter and got rid of it , but it wasn't 50% off yet. However, that seems to be a problem with many hobbyist level colorimeters and one reason I won;t be purchasing any more after trying both Spyder3 and then the D2.
Claims are made that the "latest and greatest" are not prone to drift or somehow guaranteed but I won't waste my time and money on anymore consumer or hobbyist grade meters. They will give you charts, numbers, and readings. . . but you will never know if it is really accurate.
It's a nice hobby and you can gain insight to what makes a TV picture good, but it isn't to give you the known and stable accuracy of professional mutli thousand dollar equipment. Besides, most TVs today are much better out of the box and can supply excellent picture quality using the AVS HD709, Disney WOW, or Digital Video Essentials disc to give you Media Assisted Settings.