I have entered a few orders in TWS as combo orders and they use LMT + MKT orders. I have to say that they work really well but I am not sure if this can be eventually be integrated in PTL trader. Its good for less liquid pairs, or to enter a bit better by choosing your limit price.
IBs definition:
LMT + MKT, where one or both legs are submitted as marketable limit orders when the combo becomes marketable. If only one leg fills, the second leg is resubmitted as a market order.
