My understanding:
You can't increase the Reserve above 20% (actually it might be fixed at 20%). I consider 10% sufficient as my power cuts are either
a) a couple of seconds
b) 4 hours when someone digs through a cable in the road (20% reserve not enough for for me in that instance)
c) Scheduled
For Scheduled, i.e. known in advance, I increase the reserve to 100% ... but you can't do that on TEP (except for Storm Watch where it will do that for you - whether you have TEP or not ... and when gets the Storm Watch notification it will immediately start charging to 100% (regardless of tariff, and IME that occurs a long time before the threat, so could probably / usually delay and take advantage of Off Peak). Maybe for the couple of times a year I get Storm Watch I'm overthinking that!
You can't "dump" any excess to avoid Export e.g. to Immersion or using Zappi to trickle charge the car, .
From what I have read of TEP what I hear is that it exports during the evening. My house consumption is high, and I will fully discharge my batteries from when the sun goes down until midnight ... so if I was exporting during that time I would have to buy-back energy later in the evening. Export and Import are priced the same (ignoring losses) so maybe that is moot, but I haven't got my head around it. If it means better utilisation of North Sea Wind (i.e. less curtailment) I guess I'd be happy with that.
People whose usage allows them to charge their PowerWall overnight and then it lasts them the whole day, until next off-peak rate, would be disadvantaged (by TEP) because currently buying at, say, 7.5p Octopus cheap rate and charging the battery to last the whole day, but under TEP would buy at 12p rate - albeit any time of day or night. (That's probably moot because you need PV for TEP ... but I suspect a similar "I don't buy from Grid during the day" users, with PV, exist)
I don't think the extra cycling of battery, under TEP, is a worry. Particularly if, basically, TEP discharges during evening - that's charge-once / discharge-once a day, which is what most people probably do anyway.
I've had PowerWall for a while, but only enough PV to need to do something about "Export" recently, so I haven't found an optimum as yet, but I'm beginning to think that I need a car with bidirectional charging so that I have a much bigger battery available for a) days with superb sunshine and also b) the ability to do some decent arbitrage on export prices ... but for that route I will want to keep the money, not to give it to Tesla