AUM were also 150bhp 5 speed, and had the ko3S. needs an engine code to determine what it'll be mate.
ko4 - no less reliable than any ko3 if it's done right, after all, they were standard on the S3, LCR, and TT, people just tend to cut corners and run into issues.
K04 is well worth while I believe, you get a huge range of bolt on parts for tuning, and the option to fit a hybrid down the line with potential for 330bhp+.
Price wise, ko4 setups seem to go for around the £500 mark for a turbo and manifold with a few associated parts, have a hunt around.