Seat insert for a P&Ts sport?

[HeadFairy]

There are lots of P&Ts sports where we live, I keep seeing people with something that looks like a seat insert in the top seat, so that the toddler sits higher up. I can't see it on the P&Ts website, what's the purpose of them? Is it worth getting one?

Do you mean like this? Bottom left picture.

this

It is the second seat attached to the top of buggy so second baby can lie flat.

Sorry, long delay, been out all day! yes that's exactly what it is.... Is that something that comes with the newborn add on bits?

it is the Doubles Kit that you buy separately to the main buggy, if you want to use it as a double. The seat is attached to the front (as in the picture) so that a new born can lie flat in the main buggy. When the baby is old enough to sit, the seat is moved to the back as in the picture bottom right.
I imagine that the ones you've seen had a baby hidden away at the back!!

aaaaahhhh (lightbulb moment) I see. I hadn't particularly noticed the newborn underneath but I bet that's what it is.... even if there isn't a new baby underneath I think sometimes some people keep those little extra seats as they give a bit of a height boost.