Mostly state 11+ schools use one exam per county, so all the Glos schools use the same 11+ exam which is taken on the same day, and all the Kent schools use same exam taken on same day etc
You usually only get different exam days and different content if you are taking exams for 2 different counties, or if you are taking 11+ exams for private schools, which are completely different.
exam content (for state grammars) is supposed to be the KS 2 curriculum and not beyond. So everything which is taught in year 5 and 6. That does mean that some things may not have been well covered in school, but are on the test, or not yet covered given that the test is taken at the beginning of year 6.
This is most noticeable in maths. Key things to look for
percentages
ratio
mean
You will find in many practice papers that they include median, mode and probability, but these were removed from the primary curriculum about 7/8 years ago and should not appear on 11+ papers, despite them still appearing on the practice papers.
Commercial mocks are a great idea, the experience of going to a strange place for an exam with strangers is scary, and doing a practice run (or two) is really helpful.
online mocks may be useful for looking at their standard, but not helpful with the whole exam experience that they need.