Yea, I think a griddle would be necessary on a two burner hot plate for the very reason you stated ' distribute heat evenly' and the hot plate alone would not be large enough to flop the paddles open, and keep them heated, they would flop past the stove and be at a 90 degree angle. Be tough to put batter in them. ;) Need the width of the flop griddle when opened to find a suitable long griddle.
Once these get going it is cool. Fill the paddles, brown that side, flop it to the griddle, open it, fill up with batter and keep cooking.
Theres one of these on ebay and with shipping I believe it's darn close to $45, and it's not all that nice.
The one on ebay sold, and would have been $44.96 shipped to me. I was wrong on the condition. After really checking out the pix, it was well used and not abused.