I have a pair of the very light and buoyant alpha fins.
I sometimes wear them but don't kick when wanting to concentrate on arm timing. I found it more natural than squeezing the pull bouy between my legs.
It also allowed me to slowly introduce a small flick with each leg and help with my 2BK timing. The feeling if speed was also great and emphasized the benefit of a good pointed foot kick. I found that the few lengths that I did with them really helped with my balance.
I still do a free 100s with them most sessiona.
This video was before I improved my arm timing but does show these fins in action relaxed no kick first and then with a bit of a kick.
Hope this helps.