You asked if execution speed is acceptable for scalping. The answer being yes.
It's all the "other" things that make IB not a good choice for futures trading, IMO, unless IB has a hard-to-find product offering you want to trade.
1) As mentioned, due to the "snap-shot" nature of IBs data feed, it may not provide you with accurate data for your techniques.
2) Generally speaking, IBs commission structure for futures is not that favorable. If using Un-bundled rates, the tiers are not cummulative... each tier price applies to each tier volume. Cummulative volume moves you from tier to tier, but each tier is priced independently. If using bundled rates, there are plenty of brokers offering lower rates, particularly if you are willing to negotiate. IB does not negotiate commissions. period.
3) Be very aware that IB has a habit of making frequent adjustments to intraday margin requirements, unrelated to margin changes issued by exchanges. IB wants to protect itself, in the guise of protecting you from yourself based on IBs take of market conditions.
4) Be very aware of auto-liquidation. Without warning, and before RTH close, IB will re-calculate margin for open positions. If your account is light based on the fresh calculation, regardless of your intention, IB can,will, and does liquidate positions. Again, this happens BEFORE *RTH* market close, not during after-hours. On the inverse, intraday margins, if available, kick-in AT market open. 9:30am EST, not 9:29am EST.
5) Good luck getting hold of a trade desk to resolve an immediate situation.
Never been, past or present, an IB client, not cheerleading, not axe-grinding. Just the way I see it and have heard of it to be.
Good scalps to you.
Osorico