Right. I've now had my fin for two and a half weeks and can probably give it some sort of a review.
First, build quality is extremely good. A lot of time has been put into getting things right, especially in the footpocket area. Speaking of, they are very tight but unlike my leaderfin they don't have any pressure points. I'm able to wear the fin for 20 minutes at a time and a few minutes in between is sufficient for recovery. This is a competition fin, so that's what I was hoping for. I asked for it to be comfortable for 15 mins and bearable for 30, so that's pretty much spot on. I asked for 25 degrees angle and slightly buoyant and that's what I got. My body position in the glide is now much better than it was before. I asked for a soft blade and got something a bit stiffer than I wanted, but not unreasonably so.
In the pool, I found that despite the blade being stiffer than expected I was using less energy per length and fewer kicks, despite average pace increasing. That's a pretty good combo. I haven't attempted a PB yet, but on the couple of longer swims I've done the lactic load and hypoxia was lower than with my old fin. I did notice that the lack of side rails or stabilisers on the fin itself means it's more prone to slipping sideways in the water, though only really an issue on the first kick after a turn. I'm fairly confident to say now that it is a superior fin to my now retired one and I'm a happy man. It is definitely designed as a performance/competition fin rather than a 'fun' fin, but that's what I asked for.
So, a list of pros and cons.
Pros:
Very good power transfer
Footpockets have no pressure points
Fin almost exactly what I asked for
Cons:
Blade slightly stiffer than wanted
Lack of side rails reduces fin stability
I may attach some stabilisers to the fin to deal with the last con, but honestly it's not a big issue. Alex was fantastic to work with and the fin was posted (very well packaged) when promised and didn't take long to make. I doubt there's such a thing as a perfect fin, but I have no qualms about recommending Starfins. Thanks Alex!