I am evaluating the purchase of an ESI ES-2000 for calibrating my NX-7. How stable is the calibration of these units? I see several available on eBay for around $400 that seem to have been manufactured in about 2013. I found some information on the manufacturer site that recommend annual calibration but also said 3-5 years between calibration was possible. In either case it seems likely that anything from eBay will need calibration. I also found a quote on the manufacturer site of $500 for calibration. That definitely affects the affordability and usefulness of this device if it is accurate.
I did go ahead and purchase a Spyder X for grayscale calibration but I am left wondering how reliable an ES-2000 from eBay will be,
When you are looking at the certification information I think you need to understand the context.
First off, sending the meter in for re-certification does not change the meter. It only gives you a new piece of paper telling you the status of the meter and if it's still accurate, and how accurate. If it;s not accurate anymore that's a whole separate process and cost to get repaired.
Also you are talking about meter certification for color critical work for the content creation industry. Where it's very important that things are super accurate. You really don't need that level of accuracy and certification for personal consumer home use.
That being said, these meters have an internal self-correction feature. Before each use, they illuminate and measure an internal phosphor and will self-adjust if the reading has slightly shifted or give you an error if it is drastically wrong.
I have compared earlier versions of the i1 Pro (original model, not Pro 2) from circa 2008, to modern i1 Pro 2 from circa 2016, and the reading was the same. The dE was less than 1 difference. There is no reason that these units will shift over time by any noticeable amount (for personal home calibration).
You are paying $300-400 for the meter and it's given accuracy level. By all means, if you want that extra 1-2% accuracy (that if you ask me will be imperceptible to the naked eye on screen), then you can spend the $1000+ on a newer meter, but I wouldn't go that route for home projector calibration use.
Now if I was running a professional photo studio for instance and needed to calibrate my editing monitors and printers, I would consider the new unit and get it re-certified every few years.