I've been trading with fins for about 8 months - on and off- it is very easy to amend your stop. Simply go into open trades and it tells you how.
I have NEVER had a stop go beyond what I stated with fins. It has always been exactly what I placed.
I am now also dealing with D4F, purely because they trade some shares out of normal hours, and, believe me, their 'stop system is not easy to understand. I also find their statement system a little convoluted (sorry, swallowed a dictionary), but I am coming to terms with it now.
Once I am able to trade during the day I will certainly be looking at fins rolling shares and giving them a go.
Best of luck with your trading, the best advice I can give is keep it small and ALWAYS place a stop - it has saved me heaps.