I used this a couple of years ago and it was pretty good, but takes a lot of work to put on properly, first have to thoroughly clean the screen, degreaser and paper towel job, then apply and buff off - lengthy and physical job (if you're getting on).
now I have 2 x 1kg silica moisture absorbing bags on the dash that you can dry in the oven/microwave like these
Fifth Gear 2 x 1kg Silica Gel Car Dehumidifier, Dry Air, Reusable Moisture Absorber Bag, Automotive Dehumidifier, Keep Windows Fog-Free. Prevents Condensation and Mold, Includes 2 x Anti Slip Mat: Amazon.co.uk: Car & Motorbike
also remember that the best way to demist is
1. Aircon ON
2. air vents up onto windscreen
3. max heat
4. max air flow
5. keep All windows shut and set to internally recirculate (to suck moisture out of air inside the car and not suck in more moisture from outside)
6. rear screen heat demist on
7. mirror heat demist on
8. try not to breathe too much
key criteria for next car = heated windscreen LOL