I would be a little carefull. The old gag of free trial lessons, many training providers have tried this before. The usual small print will stipulate that the trial lesson is free as long as you will accept a course of training and start your PPL.
So when you walk into the training provider and state at the front desk " I'm here for my free trial lesson, I have not brought my wallet and is it ok to fly because I'm partially blind ".
Just see how quickly the weather changes and becomes unsuitable to fly or the aircraft goes tech.
Don't you just love some training places that try anything that they can.
Good on them, trying to keep the industry ticking over.
fluffy