If you are talking about index futures, no problem. If it is cfd index or something similar, they will cheat if you are profitable. What happend to me was when i traded danish stock cfds with them was, if i made a order to buy 1000 cfds that order would change a position of 10000 cfds. Same will happend when i tried to close a position of 1000 cfd suddenly i was short 9000 cfds. Other thing that happend was if the position goes against me i wouldnt be able to close the position either by when i press sell to close the position and nothing will happen or by the order entry box would simply disappear when the position go against me, so i have to call them to fix, by then my loss would always be huge. I ended up closing my account after 5000$ loss.
I had similar problems when i traded cfds and forex with oanda, my stop loss wouldnt trigger price will go through my stop loss without triggering it, platform disconnection if i have open position and stuff like that. Do yourself a favor and dont trade with a bucketshop.