Agree As Muhammed rightly says, and I would add if the August doesn’t really suit you can always extend for 2years then end at any point after your August lease date you still receive your £600 full term bonus , should you keep it for a full 4years you receive £700 and then if you still decided to keep it and went full 5year Term you receive £900.
So for instance if it suited to end your lease the following spring you can, as you would of gone over your 3year term but not over 4years you receive the £600. At present anyone taking a 2year extension can change/terminate at any point within that extension with no penalty.