If you already have a rent figure in mind, check it against the market before you serve it. The free checker shows whether the increase looks supportable, borderline, or likely to need stronger preparation.
It is easy to calculate the monthly uplift. The harder question is whether that uplift still looks sensible when it is compared with similar homes nearby.
Before you serve Form 4A, you want to know whether the market evidence supports the proposed rent and whether the file should stay on the Standard route or move into the Defence route.
If the rent sits in a supportable range, you can move into the Standard Section 13 pack with more confidence. If the figure is high against the evidence, the safer move is to prepare for challenge before the notice goes out.
That keeps the paid step practical. You are not buying a pack because the page says so; you are choosing the pack that matches the risk in front of you.