"Bucket Shop is a specifically defined term under the criminal law of many states in the United States which make it a crime to operate a bucket shop.  Typically the criminal law definition refers to an operation in which the customer is sold what is supposed to be a derivative interest in a security or commodity future, but there is no transaction made on any exchange. The transaction goes 'in the bucket' and is never executed. Without an actual underlying transaction, the customer is betting against the bucket shop operator, not participating in the market." see: Wikipedia
The SEC believes that "internalization" is somehow different, and this affects ALL of your online trading, no matter what you are trading. Trades that are executed outside of the exchange, never reaching the main market, effectively hide data from technical analysis, and skew pricing. see: Not a bucket?
"... internalization hurts retail customers and market quality"