In solo mining we would need to pay a lot of gas for the solution to be broadcasted at first as they would come rapidly, don´t we? At least that was the case when 0xBTC was started. When the difficulty increases this should become less of an issue
Our contract adjust the difficulty much offten every 64 block! dynamical than 0xBTC (every 1000 block), it can avoid the transaction being clogged and waste the gas.