Quoting fictitiousfellow,
I had to disable Windows Defender in Group Policy before the installation would work, but, on Windows 10 Insider Build 14295, things are working fairly well. The odd hiccup here and there, but nothing traumatic. Installing WB Beta solved a lot of glitches.
Just an FYI... it's not recommended to utilize Windows Defender, as it is not effective (it never has been). Even the more improved version shipped with Windows 10 is not remotely trustworthy in preventing malware/viruses.
Been using Microsoft Security Essentials/Windows Defender since it's inception and have never had a virus/malware/trojan or anything else get through. Don't believe all the BS other AV/Malware companies tell you, they would say anything to promote their own products.
That information isn't from competitors... in every independent test conducted on the efficacy of AV programs' abilities to detect malware/viruses, Windows Defender/MSS has never broken 90% (the Windows 8 version was something like 56% detection).
Is it likely Windows Defender/MSS will continue to greatly improve on Windows 10 to the point it's on par with other competitors and scoring a minimum 95% (98.5 - 99.99% preferable), absolutely... but it isn't even close to being there yet.
I appreciate your perspective and experience thus far, however you're either extremely lucky, have good browsing and installation security etiquette, or have been been infected by malware and you simply don't know (the probability of the latter goes up substantially if you've relied only on MSS for malware/virus protection, especially if used exclusively prior to Windows 10 since you don't know what you can't detect).
Having been a PC/Network Technician for many, many years before being forced to retire due to disability, I simply use common sense browsing and there isn't any Malware or anything like that on my computers. I can boot to 7, 8.1 or 10 and there isn't anything on any of them in the way of a virus, etc. As far as independent testing.... well, lets just say that scores can be manipulated. Not saying it did/does happen, just that it can happen. I don't review independent test results on anything anyway. 
Each is welcome to their opinion, but believing independent testing by multiple parties isn't reliable is idiocy... there's forums for tin hat conspiratorialists, this isn't one of them, and attempting to pass off such quackery is unacceptable due to the extremely serious consequences involved. By your rationale, UL isn't trustworthy or reliable, so you may want to rethink having electronics in your home, electrical wires in your walls, or the concrete supporting any building you enter.
I'm not too sure why it is anyone would believe that because they worked in the IT field they're immune from viruses and malware, however it's that hubris that often belies most older technicians over 60 I've had encounters with. How it is one could work in a field where things are always fluid and never stagnant, then believe the field is stagnant around them is beyond baffling.
Perhaps I'm missing something, but being a PC or network specialist/admin does not mean you're a coder or programmer (in fact, it's a good bet you're not), as no coder or programmer would believe they're not susceptible to an exploit written by another programmer. Generally, when the word "technician" is involved in IT, it almost always refers to something to do with hardware, not programming/coding. (This shouldn't be interpreted as a slight against technicians, nor negate the importance of technicians, as technicians are an invaluable commodity to us all.)
Generally, I wouldn't post such an off-topic reply, however anyone trying to sell another user quackery in regards to IT security should never be tolerated and always confronted because of the enormous consequences that could, and most likely will, arise should someone take heed and listen to said quackery.
