@Abs_max Personally, I am also dabbling (unsuccessfully) in daytrading, and I am toying with the idea of programming my own ETF (market-capitalization-weighted portfolio). For the pure Mustachian, the use case would be broker diversification. And then I guess I just like seeing and testing for myself, after reading all I can online (I find the differences in the signup- and trading-experience very interesting). So far it has been a bit of a lonely experience, but reading this forum it seems like there are some very knowledgeable people around with tons of experience to share :).
Based on my research, right now Alpaca would be cheaper than IBKR (but of course much less established).