That is called a Boardman feeder. It won’t work without some adaptation because of the “lip” at the entrance of the Flow hive. Personally, I don’t like them anyway - as they are not enclosed by the hive, they can encourage robbing, which is very bad for a weak new colony of bees.
I prefer in hive or hive top feeders. My favorite is a pail (bucket) feeder like this:
Invert it over the inner cover of your brood box, and put the empty Flow super on to enclose it. Then put the roof on top. For that one gallon pail, 5lb white sugar and 5lb of water will make almost exactly one gallon of spring feed for your bees.
A more expensive, but very nice option is this feeder:
I have had problems with Argentine ants using this feeder in southern California, so if you have ants, make sure you make some kind of ant moat before you set it up.
One final thing, you may not need to feed at all, depending on when your bees arrive. If they are coming in April, I suspect you may have enough nectar flowing for them to feed themselves, but you would do well to ask advice from beekeepers at your local beekeeping club.