I am very pleased with my turbo timer.  I use it more than I thought I would.  It is great for times when you are on the run and don't want to sit in your car and wait for you turbo cool off.  I installed it myself and wish that I hadn't.  It will probably cost a lot to get one installed on an A4, but I would happily pay someone who knows what they are doing for the install.  I didn't hook up the parking break feature or the speed sensing features so I can't comment on them.  You can program music on this turbo timer, but I turned mine off because I like to listen to the motor before I leave it unattended.  It is also a good timer because the count down display is red, which matches the dash lighting.  I would recommend this timer because it has a very good price, matches the car well, and it has performed its basic function without any troubles so far.