I want to install iOS 7.1 beta 2 on my iPhone 5?

I heard many users without a UDID are having activation issues (at the startup screen it says 'your iphone is not registered with the apple developer programme'.So I guess I need a UDID for that…
So my first question is this:
There are many websites that provide 'instant UDID registration'. Are they trustworthy?
For example- regmyudid.com
And my second question:
Once I have registered my UDID, do I have to install it using iTunes (Downloading a dmg from a non official website and then installing it using iTunes) or can I just do an OTA update?
Third question:
Are there any other prerequisites for installing a new iOS7 beta?
Any help is much appreciated.

1: I'm not sure but i have heard that UDID registration via these website is not safe.
2: You need to download and install IPSW file via iTunes, you can't do it via update. Also can't Install Dmg file you have to convert dmg to IPSW! Check this method: http://techmell.info/apple-tips/convert-dmg-ipsw/
3: Put iPhone in DFU mode beforing install iOS 7.1 beta 2. Check this mthod to restoring IPSW: http://techzend.com/remove-evasi0n-jailbreak-iphone-5s-5c-5-ipad-ipod-touch/