Will last a couple of years, but dont even try using a jetwash as it will come away. Okay alternative to doing it properly. But it tends not to set properly all the way through, so its not solid.
Would recommend getting some proper mix and doing it, although its a shit job to do. Just finished doing mine last week, took 6 weeks to get it done in small sections. Used a 4 to 1 mix.
Pre mixed concrete should be okay. But used cement mix £5 and some sand £2.70 from jewsons.
Either way hurry up and do it, cement wont set under 7c, and once temps dropped you wont be able to do it.