different leagues mate... the arc's are for mild tuning, maybe something like a self learning sard/jam ecu upgrade, probably good for upto 170bhp (at a random guess, we'll see how far i can take mine...) but a fmic is a different league. even with a small fmic you're good for 250bhp, but as said, its horses for courses. fmic is alot of effort and pipework, also a big draw of attention, so it all depends on what you're after. i'm biased obviously, but the arc's are mint, but they're also stupidly expensive. i do not know what bhp they're good for, but i'll source an ecu, up boost, and see how far mine will go before it becomes the limiting factor.