I'm skeptical towards the whole topical dutasteride thing as well. As far as I understand, finasteride and dutasteride have an almost binary response in terms of inhibiting DHT. Finding the appropriate topical finasteride dose (that inhibits DHT in the scalp, but not systemically) has been somewhat of a holy grail, with finasteride presumably accumulating over longer periods of time, despite its relatively low half-life. This complicates things because if the dose is too high, the effect accumulates and eventually inhibits DHT systemically at the same rate a regular oral dose would. Mazzarella was supposedly able to do it in a study from 1999 with a dose of 0.01% per day (or 0.005% twice-daily, to be more precise), although some people have tried to replicate it and ended up with systemic DHT-inhibition anyway.
Considering the above, I don't see how this would be different for dutasteride. Considering it's much longer halflife (and lack of topical studies - like Mazarella's - to go off of) it actually seems more difficult to me to find the appropriate topical dosage. Some are arguing for liposomal solutions, but I don't believe that liposomal formulations prevent all systemic absorption. If it penetrates the scalp, I can only assume that some of it will go systemic and starts accumulating over a longer period of time.
I'm open to counter-arguments, as I hope I'm mistaken. But it seems too good to be true. I'll post this in the topical dutasteride thread as well.