It is quite sturdy! I have two kids and it is the only way I can take them out by myself. Generally, I sit on the side when there is space and comfort, on the sidewalks of our Greece there is an issue especially if you are the weaker (physically) gender. First the stroller and in the end you can lift it by the handle where the child's bottom is with one hand... it wasn't convenient that the arms open and close at the back. Every time you turn, the child does a DRIFT. So I had to tighten them a lot, then because the brake is on the central axis that connects the board, it didn't manage to work as the central brake kept closing due to gravity. So I found another solution with a tireup.
About the screw... I was looking for the screw and ended up doing a review, I just lost it and couldn't find anything online... and I ended up in China on a well-known site with the term << M8 x 50mm Star Knob Bolt >>
Logically it's M8 but I will make sure by measuring the other one that's on it or I'll get an M6, an M8, and an M10. I'll get it right.
Finally, about the weight, don't worry, it holds 14 kilos for the child and 85 for me together.

Very good, it is convenient with a second child to sit either upright, as long as the handle of the stroller extends or at least goes up. Going up and down the sidewalks is a bit of a hassle because the child has to get off, but it goes smoothly on small ramps.

I use it every day for 1 year. Its connection is now a piece of cake. No matter what scooter you use, your feet will fall on it. I asked two moms with two different scooters and they had the same problem.

As for the screw... mine was loose at first, but then I raised the axles a bit higher, to have a little more tilt, and it didn't drag on the ground.

We added an extension to the stroller handle (peg perego book 51) and still fall on it when we walk. Personally, I walk beside the stroller so I'm not limited in my stride, especially when I'm in a hurry.

It's not easy to lift it on sidewalks, but if you lift the back wheel of the stroller with your foot, you can easily lift it from the front.

The child is tied, it is safe. My eldest (2 years old) has fallen asleep on the trolley many times for a few minutes until we get home and has not fallen even once, leaning on the head on the armrest. (if he struggles, yes he will fall tied).

The elder feels close to the baby and does not feel disconnected from the stroller. If the baby looks forward and the stroller has its back, then when he falls asleep, he cannot lie completely vertically as the seat will fall on the other child.

You can turn the baby's seat either independently to look forward or backwards to look at his sibling in the stroller.

The only thing I would like is an adjustment in the height of the seat so that the child's knees do not bend so much, especially if he sits there next year and will not be standing on the scooter.

I have not regretted it. In terms of quality, I have had it for 10 months and it seems to be durable. Yes, the screw came off for me too, but I bought a screw-nut for 5€ from a hardware store (it's not exactly the same size, but it is hidden underneath and not visible) and it works fine. What they say about it being taller for the parent's legs is not possible because the child would hit their head. Most of the time, I use it by walking on the sides. It has flaws...yes, but it's not like it can be perfect with just 2 strollers. And the child enjoys the ride.

The issue with the screw is indeed a quality matter for its price.

Very convenient and high-quality, it really helped our big baby and us, perfect for long walks.

The child sits comfortably. The only positive thing ..
Otherwise, we bought it last year, we used it on a very expensive stroller ... it didn't fit ... Then the worst thing is that it is very wide, so if the stroller is low on the handles, you have to walk bent over !!!! and your legs constantly hit this part !!!!!! ... You can't walk at all .. the wheels should be completely sideways and have more height from the ground so that the stroller driver can walk properly ....
Finally, there is a screw under the seat from the bottom side ... This came off twice ....
It's better to see it up close and try it before buying such an accessory .!!!!

The child sits comfortably. But if you have a stroller that folds with a cane, it won't fit 100%. Also, the handle of the stroller should be raised, otherwise your feet will hit.