They work, like you say this seems very expensive especially when shipping is included.
They do not need mesh. The face you see in the pic is nailed facing into the board, and an augur or disc cut hole, maybe an inch or more wide, is made in the board. Then its drilled hole facing up to the supers, plastic implement facing down to the broodnest, and clearing should be quick.
However..................bees cut off from the queen and seeking a way back behave in a certain way mostly, which makes centre exit clearing slower than corner exit. They become agitated and tend to march round and round the outer edges of the isolated boxes, and although centre exit works OK, corner exit is faster. Making oneself a New Zealand style clearer board is cheap and easy and doen not need you to buy any expensive gadgets.
http://www.dave-cushman.net/bee/canadian.html#nz
Dave referred to them as Canadian style, on hos page look for the very first pic with the four corner assembles in place.....you actually only need two in opposite corners, but four of them will clear the box above in maybe an hour at most. they are very very rapid and do not clog up like porters do. Simple to make at home. They are what we use, and the very first time we did that using some borrowed boards it was blindingly obvious that Porters were slow and inefficient by comparison. Exit over 100 porters to the bin.
ps....the plastic one CAN also be used with mesh..............driling a hole through the plastic as well and attaching it the other way up............might work faster that way.
) but I have a similar, but 8 way version, as recommended by my tutor - just in case I get opportunity to use it 
