I installed the block heater on ours, eight o’clock day one, and it’s been used before virtually every cold-start. Hopefully helps. BTW, typo in title?
Owning a Prius in a tropical climate isn't effortless... but sure am glad not to worry about block heaters
One heads-up regarding the Toyota block heater: there was a recall on ours, so I took it in for replacement, and the fix was basically that new one is absolutely anemic, raises the coolant to lukewarm tea level in about 3~4 hours, versus the old one which got it toasty in two...