Quote from def:
I disagree strongly with your statement. the front ends mentioned are far from competitors. They route directly into IB via the API and offer a product that caters to a specific niche of traders. thus they complement the TWS very well.
I can only agree with def. ButtonTrader is offered exclusively to IB-users (so no competition). And both systems TWS and ButtonTrader are used as one environment using features of both systems at the same time as if it were one integrated system.
So traders use TWS to trade some Options and Bonds and use TWS-charts, and at the same time use ButtonTrader to daytrade fast moving markets (Futures, Stocks, Forex {very soon}) for which they like the ButtonGrids and the advanced strategies, above TWS's BookTrader.
Just use what fits your trading most, and for about $1 a day you can not say it is expensive to benefit from both environments.