Before Tardis all I used was Tarminator, it does work and it does a good job the only draw back is that for really old, stubborn tar it takes a long time to work it's magic, not only that but I find I have to use lots of it to remove old, stubborn peaces of tar.
I've been fooling around with Tardis and I'm very pleased with it, removes glue very quickly...only draw back it's not so good to get it on your skin and you have to be on a well ventilated area. As far as price goes yea not the cheapest product but I'm a firm believer you get what you pay for...but that's just me