So the verdict is they work when it's just a few buzzing around but not so much when it's clouds of the blighters, and any little breeze will stop the unit from being effective for 15 minutes? My tip remains circling yourself in pungent incense. Any breeze doesn't help, but when that goes the perfume smoke resumes quickly. I've had swarms of them hanging just outside of the smoke-zone.
I just used a bog-standard pungent smell, but I should give the Citronella version a shot, perhaps 3 or 4 of them alternated with 3 or 4 more musky ones.
https://smile.amazon.co.uk/Genuine-Incense-Various-Fragrances-Citronella/dp/B07B74VD79/