SC Jalan Ampang told me similar thing as well. I just got mine changed there a couple of months back due to iStop malfunction without any cost. Its first time within 3 years.

I had one behind the driver seat and it is fine. Not that spacious but probably still acceptable. I am about 160+ cm tall.

I also had one at the front passenger seat, and for that, i had to push the seat all the way to the back and it made very little legroom. Pushing it to the front are mainly fine. Pushing it to the back will be uncomfortable to me.

Yes you will need to. Unless its a small toddler. My 3yo would need it to be pushed, if not, his leg will hit the seat.

Both does not matter in term of room, honestly. I had it on rear facing previously and front facing now. Problem is mostly putting a child seat at the front psaaenger seat, then you will need to push tht seat all the way back and that will be uncomfortable to the passenger behind.

Do you guys know whether there is anywhere that sells magnetic customize sunshade for the M3? Something like the ninja shades.