Let's talk about the third row straight up because that's essentially the big difference between this GLB 250 and say, the Audi Q3. Mercedes claims the third row will fit a person up to 168cm (5'5") tall, so it's lucky then that I'm 161cm (5'3") and can comfortably sit back there.
I know my taller CarsGuide colleagues can get back there too, not with loads of room, but they can just squeeze in. So somehow, there is space. And you know how practical it is having two extra seats in the back for when you need them to cart extra kids around or the grandparents.
The trick is that the middle row slides backward and forward, so you can customise the space. If you place the middle row all the way forward, young children will be able to fit in the middle row but no adults.
My two children, aged six and eight, had enough space to be comfortable. Taller people will want to slide the row back for a more leg room. There's enough headroom for everybody.
Space in the front is great. I really like the Mercedes cabin and the square-ish shape of the car adds to the extra interior space. There's enough leg and headroom for the tall members of my family and it's comfortably wide as well.
With the back two seats down flat, the boot is a very decent 565L, which is a good size for the small SUV category. I put it to the test this week because it was my turn to do the fruit and veg shop for my food co-op and I managed to fit 16 boxes of produce throughout the car.
Pretty impressive as I was concerned there wouldn't be enough room. You'll get suitcases in, or a double pram will fit, too.
If you're using the back two seats, the boot shrinks dramatically (same as other seven-seaters) but you'll still get school bags in there or groceries. Probably not both. I also fit a carry-on size suitcase.