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The U5855A offers excellent value for money and its image analysis software is free of charge so no problems on that front. It has a decent manual focus lens and is capable of very respectable thermography. It is a little limited by its 160 x 120 pixel resolution but in many thermography applications that is still acceptable.
The cameras were originally offered without a battery but now a Keysight include one in the deal. The power adapter is a standard design with a 2.5mm power plug connector.
The U5855A normal retail price is quite high but these Keysight factory demo units are being sold at a very reasonable price. I now own three of them (one is a repair project though). The OEM is the venerable NEC AVIO who went into partnership with Keysight.
The Keysight factory outlet also has complete kits with all accessories but these cost more. I did not need the hard case or accessories though.
It is important to be aware that some cheaper thermal imaging options are not the most accurate where temperature measurement is concerned. Phone dongle types would not be my first choice for real thermography.
On the secondary market, I recommend the FLIR Exx series for serious applications. The E40 may be upgraded to E60 spec in the same way as the E4 can be upgraded to E8 spec. That is to say you get 320 x 240 pixel resolution and all menus active. Upgrading is not always something that a professional thermographer would wish to do but it is the companies decision really. An upgraded. Amera can still receive a valid calibration check certificate. FLIR support does become an issue though.
Given the choice of what is currently available and excluding upgrading cameras, the U5855A offers exceptional value from a much respected company, both Keysight and the OEM, NEC AVIO. $620 delivered would take some beating IMHO. An upgraded E40 is superior though. But then that will cost around $1500 to $2000 on eBay.
NOTE: If you decide to buy an E4 for upgrade to E8+ spec, be aware that the latest (2017) release cameras cannot, at this point in time, be upgraded. You will be stuck with a very limiting 80 x 60 pixel resolution.
Fraser