Exhaust cut out is a valve (the best ones are boost controlled like wastegates) that opens and allows exhaust to bypass the restrictive stock system. I personally hate them because I want a good sound all the time (like borla) and they tend to leak.
Turbo timers will be a source of debate as long as they are around. If you read your manual it says that after going up a long hill, long drives, or particullarly hard drives you should allow your car to idle for approximatley 30sec. In these rare cases a Turbo Timer would be helpful.