I trade them often at IB, both long and short, but don’t have anything else to compare so not sure how to answer your question. Your question also seems too unspecific as low float stocks for regional banks may behave very differently from biotech. Shorting also works differently than going long. Hard to borrow stock also work differently than those available for shorting. Volume on low floats can be a few hundred shares per day and you can wait for fill several days depending on your limit price, while the volume can shoot up when pumped on news, etc. Every day and every stock can trade differently, while all this doesn’t depend on the broker.
But generally IB routes orders to exchanges, so fill quality and speed will be as good as availability of the stock itself. While you can have some control by trying different order types and directing orders to specific exchanges, which again, may work differently for different stocks.
Sometimes when I set the limit price to be immediately marketable and use their SMART routing, I feel like I get screwed by overpaying and my order shown as being filled at “DARK” exchange, meaning some dark pool. But I don’t know whether I would get a better fill elsewhere, so it’s still hard to compare to “nothing else”.
At least there are lots of parameters you can control: order type, limit price, routing to specific exchanges, algos, hidden orders, etc. As long as you have such control then the broker shouldn’t matter except for commissions.
Availability of hard to borrow stocks seems better than at other brokers, at least based on some people telling me they cannot short the same stocks or fill similar short orders at TDA (not even sure if this applies only to hard to borrows, as various shortable stocks may not be available for shorting at some brokers anyway).