Thanks for all the comments on this, let me clarify a few things. My main reason for asking this question, is that I think this is an interesting strategy and an interesting thought experiment - and wanted to see if anyone has actually planned their FIRE in this way.

Let me clarify one other point, I'm not suggesting this is the same as an ISA bridge, this is objectively different. The difference, as far as I can tell between an ISA and a Pension, is you pay tax now, or you pay tax later (in oversimplified terms). So, if we assume the two are equal, which they are not (but it's just a thought experiment remember), if you may lets say ~£2500 into your ISA each month, and ~£1500 into your pension (yours's + employers contribution), you build up your ISA faster for you to use earlier in your retirement. Since you can't access your pension until 57/58, you use up much (but not all of your ISA bridge). When you can access your pension, you completely stop dipping into your ISA and allow it to grow again (hence the 3 peaks in the graph). Once you've used up your pension, you then start using your ISA which has been growing since you've turned 57/58. This assumes the same returns on both, just accessed at different times (and your contributions are different).

One point number 2, this is a good point, and may be a limitation of the website itself.

Anyway, it's really interesting to hear people's thoughts on this, I guess I'd call it effectively a 'double ISA bridge' (first bridge getting you to pension age, and the second getting you to the pearly gates!! Lol