Won't give a lot more power on a naturally aspirated 8v. Probably max of 10Bhp gain.
Out and out power isn't the full story, a custom re-map can change where peak power and torqu are developed to suit you driving style and can make the car much more fun and responsive to drive.
IMO a cusotm map such as the one provided by GSR or Emerald gives better results than a generic map download such as the ones provided by Angel tuning.
Also worth considering an induction kit by GSR as they will increast the torque of the car considerably in conjunction with the re-map.
Looking at £200 for a re-map + £150 for an induction kit, plus insurance costs and reduced longevity of the engine. Looking at a 5% ish drop in max engine life, should still do 150,000 miles so no major concern but something to bear in mind.
Often the cheapest and most reliable way to get more power is to buy a more powerful car.
Other like myself like the challenge of trying to improve on the original design and being original.
Bit rambling at this time of night lol but hope it helps answer your question.