lxsw20: They are extremely simple to fit your self. The one I got off TM included gel caps and the seller had even done a little diagram showing how to install.
"extremely simple to fit" can be a bit of an oxymoron.
The basis of a master filter install is simple, simply install this to split the copper where it enters the house. In the real world however things aren't necessarily so simple. I've had master filters that have taken literally 10 minutes to install. I've also installed filters in residential properties that have taken close to 3 hours to install, with a scenario in which your average person would have been absolutely lost.
I would highly reommend that people who don't have basic knowledge of phone or data cabling don't attempt an install themselves.
*Need help configuring your Linksys ATA or IP Phones for New Zealand? Check my blog post