It's always the same chance you take wherever you go. You're putting more power into an engine that you don't know the history of.
better in my opinion to take it to someone with a good reputation of mapping the FRS than plugging a DIY Dreamscience map on and taking your chance.
Personally, having seen my 3dr and my mate's FRS mapped at Sabre, I'd say you're in as safe hands as anywhere.
I've known people spend thousands on rebuilding an engine, only for it to shit itself on the rollers during a mapping session.
At the end of the day, you pays your money and takes your chances