Do you have a non wetsuit swim this Autumn/Winter, Kona even? should you factor in a swimskin from the likes of….
When I went to watch Kona in 2015 everyone was in the Roka suit but they were loaning them out to trial so not conclusive.
Swim skins are designed to obviously go over a tri suit for the swim section of your race which will streamline a two piece tri suit and probably help over not wearing one. Over a one piece I am not so sure so factor that in as to what you might race in. The saltiness of the water off Digme Beach/Kailua Bay was very impressive as we floated around drinking coffee handed out from one of the sponsors boats so for sure do not stress too much about it being non wetsuit.
You obviously take a swimskin off in transition which takes a bit of time so add that in to the eqation. Supposedly they are hydrophobic so you swim faster but most tri suits aim for this as well and are hardly full of drag in their own right. Some more compression might help if you can get it on tight enough but again it then gets harder to take off. They are not allowed neoprene so no buoyancy.
Some swear by them and use them all the time in Non Wetsuit swims. Since Speedo do not make one I have not really tested all the claims of speed gains and can only go on feedback. Most positive feedback I have had came from Women who might struggle in a tri suit only <if they have a small waist> as water might gather in the lower back. With two suits on and the outer one tight it might stop the lower back area filling. Not 100% conclusive but perhaps something less likely that men would suffer as much if waist bigger. So anatomical considerations as well!
Sorry there are a lot of ifs/buts with this
I used to use the Sailfish version years ago but that had neoprene in it and helped massively. Probably in the grand expense of Kona it is a small extra amount but it all adds up I know.
As for justifying the expense I also think it helps where you might, time wise, be exiting. If you can make a breakthrough to sub 1:10 it will help massively. The usual peak exit of an IM at 1:20-25ish now becomes 1:10 as it is the worlds and most complained how scrappy/violent the swim is at this timeframe.
Goodluck whatever you decide and I would appreciate any feedback on your experiences.