Yeah, I had a sidecar for a while on a 1969 BMW R50/2. Slower than a rock (but only slightly faster without the sidecar) and mighty cold in the Wisconsin winter. I ended up rolling it on a right-hand turn and earned a custom 3 piece wrist for my efforts to protect that helmet and the head in it.
It will be 35 years next February and that wrist still gives me problems. I should have sacrificed the helmet, it wasn't worth that much. Some say the head wasn't either.
The biggest problem is the power and brakes are to the left of the center of gravity. It wants to turn right on power and left on the brakes. If you put enough weight in the car so it doesn't roll over in right-hand turns, then the power - right and brakes - left issue gets worse. On that R50 I couldn't handle any additional weight at all and it was a very light sidecar, so the right turns were a problem. But it turned left like a sports car! And it was pretty good in the snow.
On the other hand, as Ara has shown us it can haul a lot more stuff than a solo bike. It will never tip over when parked either, and it can be parked at any angle.