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Pull a week of tick data from two different brokers for the same pair and compare. The highs and lows of each minute will differ, sometimes by a pip or more. The count of ticks will differ by a factor of two or three.

Each broker aggregates liquidity from its own providers and applies its own filters and markups. The price stream the client sees is a product of that mix. Even brokers using the same bank liquidity can show different ticks, because of different aggregation rules.

For scalpers the consequence is that a strategy tuned to one broker's data may not work on another's. A pattern that relies on a certain tick frequency, or a typical spread at some time of day, is partly an artifact of the feed.

A related point is that public historical data, from services that sell or give away tick history, is a third version. It may be from a single bank or an average of several. It will resemble the broker's data, but not match it.

Moving from one broker to another, even with the same platform and pair, means re-validating the system. A short forward test on the new account, with small size, shows whether the behavior is preserved.

Has a system performed differently after changing brokers, and was the feed the main reason?

This hit me when I moved my main account last year. I had a small mean reversion system on EURGBP that had worked steadily for about eight months, and on the new broker it went flat within three weeks with the same settings and the same platform. I assumed I'd broken something in the code before I thought to look at the data.

When I exported a day of ticks from both accounts and lined them up, the new broker had roughly half the number of updates during the Asian session. My entry relied on a fast burst of ticks as a trigger, so it simply fired less often, and when it did fire, the move had usually already happened. The spread profile by hour was also slightly different around the European open.

Now I treat any broker change as a new system. I run the old and new accounts side by side at micro size for at least a month before moving money, and I re-tune only the parameters that depend on tick frequency, nothing else.