Derv units can be fun, plus the shunt of torque is quite addictive at times! For a 140BHP unit, remapping gets you roughly between 170-190 BHP depending on the engine, a stock 170BHP should break the 200BHP barrier easily on its first remap. My Uncle's 140BHP unit was Revo mapped and ran 190BHP on the dyno. That was before he added the Milltek exhuast so it's probably touching standard GTI territory now. For more power and you probably looking changing a few things like the intakes, clutch and others.
Best of all it costs peanuts to run, I can't believe I pay £200 to tax my lathargic 1.6 compared to £140 for his torque monster.