I can’t see what advantage the bloke gets from them.
Potential advantages are that you don't have that awkward period of putting on the male condom with the associated issues of loss of erection etc. The female condom can be inserted well in advance even hours. You don't have to withdraw once you have ejaculated although that's less likely to be relevant with punting? Many say it feels more natural ... others disagree.
I only ever tried the older versions which were likened to shagging a crisp packet especially in terms of noise. That was my experience also but the FC2 versions are nitrile and are allegedly much quieter?
Being nitrile they can be used with almost any variety of lube and don't suffer the dryness effect of latex which can lead to rupture. I gather they are popular with anal (especially MM) for this reason, but they are not actually approved for anal sex, partly due to lack of research.
The female condom was supposed to be all about feminism and women taking control but it just hasn't really happened?
If used correctly they are slightly less effective in relation to birth control but not significantly so. They do prevent STI's on a par with the male version and some claim they give increased protection against skin to skin transmission of HPV and Herpes, but that's theoretical and opinions are split.
They require practice to insert on the part of the female but once mastered this is not considered a problem by those who use them.
The really big disadvantage is the risk of the penis going 'down the side' instead of within. It can happen accidentally if not enough care, but more importantly with punting may be deliberate with 'the BB seekers'.
Rather like the general population they just haven't caught on in the punting world either .... but a small number do use them?
Finally if you are turned on by the sight of female genitalia as part of your session then this may be diminished by the view of the outer ring of the condom?