I think it’s the wrong question. It’s comparing two different manufacturers, their models all based on one pretty irrelevant feature. I’ve not heard much about either car as they’re both relatively new but here’s my thoughts:
Frontera is a Stellantis car and doesn’t seem a particularly efficient shape. Expect the actual mileage to be a lot worse than you’re being given on WLTP. The ‘Extended Range’ is a joke, that’s all the way up to a 54kWh battery that’s 125 miles at motorway speed in winter, that’s not what I’d be calling extended range and worries me what the other achieves. If you’re planning on using that to see family at Christmas, look for a better car.
The E-Vitara is brand new, it seems well spec’d and looks like Toyota/Suzuki’s usual rugged identity. A 61kWh battery will give you better results, claimed 265 miles but expect 180 ish in winter. Standard range is only 49kWh and with that body shape, I’d not expect miracles for range.
I usually suggest a 60kWh battery minimum unless you want to stop every 2 hours for 40 minutes. The problem is smaller batteries usually come with lower charge rates, so still take the same sort of time to charge. Imagine how good they’ll be charging 50kWh at the rate that takes an Enyaq’s 82kWh to 80% in 35 minutes…
Now, as for the Heat Pump you’re saving 5% of the heater’s draw by using a heatpump. Even if you go hyper efficient and find one claiming 10% it’s still only the draw of the heater and in certain conditions you’ll get the best output. While the weather will change, you’d need the heater blasting forth for days on end in winter for 3 years to see any value from it but that’s not the comparison today. It’ll help with efficiency a little but I’d ask if you prefer the Suzuki over any Stellantis car before worrying about whether the heat pump will make a difference, there’s too many other variables that will also make a difference between the two, like motor size and efficiency, how well the battery is managed, airflow, tyre resistance, etc., I’m not sure comparing the two even resembles comparing eggs with eggs.
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I'll try to give my honest opinion but am always open to learning.
Mark