It doesn't work like that. TT, CQG, CST they are just routing your trades, providing technology for that and they have their infrastructure but there is also broker/ FCM involved in all that.
You can have same routing technology (let's say CQG) working perfect for spreads/flyies etc. with one broker/FCM and working crappy with another one. And it's your money that can be affected by those problems.
I.e.g. - if you want to trade exchange traded spreads, how your brokerage's risk department calculate your position and your pnl ? based on spread itself as a product from ets or maybe based on legs ? There are many products that are liquid and "heavy" on spread exchange products ladders, but not very liquid in outrights ladders. If outrights ladders go dry before close or after opening, what will happen to your position ? What do you think ? What with position/pnl calculation for synthetic made from correlated products with margin credit ? Another example - how is margin calculated for your synthetic overall ? In different points of time (when you enter your synthetic position, when you are in trade, adding to it, when you closing it, etc.) ? Let's say you trade synthetic spread but that combination has some span margin credit, for routing it's no problem, but are you sure it is working fine on your brokerage/FCM side ? If not, are you sure you won't have any problems with legging in ?
If you want to trade spreads do a research and use company that is suitable for trading spreads. You will save yourself a lot of troubles and money.
Beside all that, spreads are interesting products and I wish you good luck in your journey

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