I purchased those kind [Mann Lake though] and used them for a while, but don't use them much anymore. The floats may "float" better in sugar syrup rather than in just water. I used some wood bars as floats and yes they have to be short enough so they don't get caught up and hang above the syrup level. I had too many bees drowning. Some beekeepers use hardware cloth folded in. Some styles use caps and small ladder tubes going into the syrup. Sometimes the bees build comb inside of them. I wonder if these were developed before top feeders were,. "invented"? 
In the early spring when they are placed on the far outside, the syrup seems to get cool and mold forms on that side of the box.
They may work very well if you have a lot of colonies and can just pop the covers and fill them with a hose from a 50-100 gallon tank on a truck? Easier to store also. Eventually you have to replace with frames.
There is no "perfect feeder". Even though I need an extra box, I like the plastic buckets or even the Boardmans inside. For feeding a lot of gallons in the fall, [If needed] I like the top feeders. Now that you got'em,. no harm in trying them and see how you like them though.
In the early spring when they are placed on the far outside, the syrup seems to get cool and mold forms on that side of the box.
They may work very well if you have a lot of colonies and can just pop the covers and fill them with a hose from a 50-100 gallon tank on a truck? Easier to store also. Eventually you have to replace with frames.
There is no "perfect feeder". Even though I need an extra box, I like the plastic buckets or even the Boardmans inside. For feeding a lot of gallons in the fall, [If needed] I like the top feeders. Now that you got'em,. no harm in trying them and see how you like them though.
