Two separate things often bite at once when people move onto a smart or EV tariff, and it's worth separating them. The first is the higher standing charge: smart and EV/night tariffs frequently carry a dearer daily standing charge than a plain 24-hour plan (the cheap night units are partly paid for by a higher fixed charge), so even before you use a unit you're paying more per day. That's the trade-off for the cheap overnight window — it only pays off if you genuinely shift a lot of load into that window.
The second is "level pay" — a billing method (offered by some suppliers) where you pay a flat monthly amount based on forecast annual usage, rather than paying your actual usage each month. It smooths out the bill-to-bill swings, which solar homes get a lot of (tiny summer bills, big winter ones), but the "initial sting" people describe is that the forecast can run ahead of your real usage for a while, so the early payments feel high before any over-payment is reconciled. It's a cash-flow smoothing tool, not an extra charge — but it can feel like one until it settles.
The practical advice: don't judge a smart/EV tariff on the standing charge alone — model the whole package (standing charge + day/peak rate + the cheap-window rate) against how much load you can actually move overnight, using your downloaded half-hourly data. And go in knowing level pay front-loads payments before truing up. For a battery-and-EV home that charges hard overnight, the cheap window usually wins comfortably despite the higher standing charge; for low overnight usage, it can come out worse.