I worked out when JLR stopped allowing Intelligent Octopus directly with the car, that it was still better for me to install a compatible charger, especially as I already had the necessary cabling in place, it just needed a different charger. My Zappi works with both Intelligent Octopus Go and Agile Octopus, and if I need a full 13 hour charge, then I get 13 hours at 7p/kWh which is where the saving to pay for the charger comes in. The other advantage of a compatible charger is that it doesn't matter which car I'm driving, so when I change cars, or if someone comes to stay that needs a charge, they all work. I've also benefitted from several free hours of charging with Octopus in the last month or so when there's plenty of renewable generation.
I do a lot of miles, 20k a year, so need as much low cost charging as possible. If you don't to do many, and can charge every night within the 5/6 hour window, then the extra cost probably isn't worth it.