Opinions on the Doona

I’m after opinions on the doona car seat/pram combo. I know there’s other brands available but this the main one I keep seeing.
I have a travel system already where the car seat does come off an isofix and goes onto the pram base…but it’s huge. So I either buy a new travel system or I look into the doona. I’ve seen them advertised and like the look of them but I am genuinely questioning the safety aspect.
It will mostly be used for school run with my older child not for baby to use as a main pram and be in all the time as I am aware of the risk long periods of time in car seats pose. But, to save me having to take the whole travel system with me for school runs, the doona would be ideal.
Also, I would be buying one second had (probably) which is also risky.

So basically, are they worth it, or should I just suck it up and use the (kind of heavy and bulky) travel system I have.