There doesn't appear to be any detail on the BG website about the specific tariff that this would be attached to, but I think it's a relatively safe bet to assume it would be their Electric Driver V2. For me, the rates are these:
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They have a 5 hour off peak rate 00:00 to 05:00.
It's slightly cheaper than the current Octopus Go rates of 30.6p & 9p per kWh (00:30 to 04:30 off peak). Standing charge 47.95p.
If you do a lot of mileage, Intelligent Octopus may work out a bit cheaper overall but it would be borderline with the 12 months free charging with BG. You'd need to run the numbers for your usage pattern. I'm not sure what the rates are on that right now. I only do around 5-6000 miles per year at the moment and work from home (lots of power use all day), so for me Octopus Tracker is still far far cheaper. My October bill had average electricity of 17.47p per kWh for the month for all usage. And 5.24p per kWh for gas. There was a waiting list for Tracker, I'm not sure if there still is.
It's quite tricky to work out which tariff would be cheaper unless you have a decent idea of your usage split daytime vs overnight and how many miles of charging you'll be doing at home. Getting charging at work makes a fair bit of difference of course, as would needing to use Superchargers instead of home charging.